MimeKit

MimeKit

Package	Latest Release	Latest Build
MimeKit
MimeKit.Core
MimeKit.Cryptography
MailKit

Platform	Build Status	Code Coverage	Static Analysis
Linux/Mac
Windows

Obsolete Packages:

Package	Latest Release
MimeKitLite
MailKitLite

What is MimeKit?

MimeKit is a C# library which may be used for the creation and parsing of messages using the Multipurpose Internet Mail Extension (MIME), as defined by numerous IETF specifications.

Upgrading from MimeKit 4.x? MimeKit 5.0 contains a number of breaking changes. See the Porting Guide for step-by-step migration instructions and the Release Notes for the complete list of changes.

Contents

• Donate
• History
• Performance
• License Information
• Installing via NuGet
• Getting the Source Code
• Building
• Using MimeKit
  • Parsing Messages
  • Getting the Body of a Message
  • Converting HTML to Plain Text
  • Converting Enriched Text to HTML
  • Traversing a MimeMessage
  • Quick and Dirty Enumeration of Message Body Parts
  • Getting the Decoded Content of a MIME Part
  • Extracting TNEF (winmail.dat) Attachments
  • Checking Messages for MIME Compliance Problems
  • Creating a Simple Message
  • Creating a Message with Attachments
  • Creating a Message Using a BodyBuilder (not Arnold Schwarzenegger)
  • Initializing MimeKit’s Cryptography Support
  • Preparing to use MimeKit’s S/MIME support
  • Preparing to use MimeKit’s PGP/MIME support
  • Encrypting Messages with S/MIME
  • Decrypting S/MIME Messages
  • Encrypting Messages with PGP/MIME
  • Decrypting PGP/MIME Messages
  • Digitally Signing Messages with S/MIME or PGP/MIME
  • Verifying S/MIME and PGP/MIME Digital Signatures
  • Signing Messages with DKIM
  • Verifying DKIM Signatures
  • Signing Messages with ARC
  • Verifying ARC Signatures
  • Verifying DMARC
• Contributing
• Reporting Bugs
• Documentation
• .NET Foundation

Donate

MimeKit is a personal open source project that I have put thousands of hours into perfecting with the goal of making it the very best MIME parser framework for .NET. I need your help to achieve this.

Donating helps pay for things such as web hosting, domain registration and licenses for developer tools such as a performance profiler, memory profiler, a static code analysis tool, and more. It also helps motivate me to continue working on the project.

History

As a developer and user of email clients, I had come to realize that the vast majority of email client (and server) software had less-than-satisfactory MIME implementations. More often than not these email clients created broken MIME messages and/or would incorrectly try to parse a MIME message thus subtracting from the full benefits that MIME was meant to provide. MimeKit is meant to address this issue by following the MIME specification as closely as possible while also providing programmers with an extremely easy to use high-level API.

This led me, at first, to implement another MIME parser library called GMime which is implemented in C and later added a C# binding called GMime-Sharp.

Now that I typically find myself working in C# rather than lower level languages like C, I decided to begin writing a new parser in C# which would not depend on GMime. This would also allow me to have more flexibility in that I’d be able to use Generics and create a more .NET-compliant API.

Performance

Performance has been a core design goal of MimeKit from the very beginning. MimeKit’s parser works directly on raw byte buffers rather than first converting the input into strings or splitting it into lines, which keeps both CPU time and memory allocations to a minimum. Some of the techniques it relies on:

• A low-level, allocation-conscious streaming reader (MimeReader) that the higher-level MimeParser builds on.
• Pooled buffers and lazily-decoded headers so that only the data you actually access is ever decoded.
• Hardware-accelerated (SIMD) scanning and base64/uuencode encoding and decoding on x64 and ARM64 platforms when supported by the runtime.
• Source stream storage (MimeParser with storage: MimeContentStorage.Source) so that MIME part content can reference the original stream instead of being copied into memory.

The result is a parser that can comfortably process very large messages and multi-gigabyte mbox files while remaining spec-compliant and resilient against malformed or malicious input.

Long before .NET Core made SIMD available to C# developers, MimeKit was already fast thanks to a number of parser design choices and optimizations that are described in more detail in the following blog posts:

• Optimization Tips & Tricks used by MimeKit: Part 1
• Optimization Tips & Tricks used by MimeKit: Part 2

If you are curious about the details, the Benchmarks directory contains a BenchmarkDotNet suite covering the parser, encoders, decoders, filters and more, which you can run on your own hardware.

License Information

MIT License

Copyright (C) 2012-2026 .NET Foundation and Contributors

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

Installing via NuGet

The easiest way to install MimeKit is via NuGet:

dotnet add package MimeKit

Or, in Visual Studio’s Package Manager Console:

Install-Package MimeKit

MimeKit is split into the following packages:

• MimeKit.Core - MIME parsing and message construction, along with everything else that does not require cryptography (address parsing, encoders and decoders, HTML, RTF and text converters, TNEF, etc.).
• MimeKit.Cryptography - S/MIME, PGP/MIME, DKIM, ARC and DMARC support. It depends on MimeKit.Core and BouncyCastle.
• MimeKit - a meta-package that references both MimeKit.Core and MimeKit.Cryptography.

If you don’t need any of the cryptography features, you can reference MimeKit.Core instead:

dotnet add package MimeKit.Core

If you do use the cryptography features, see Initializing MimeKit’s Cryptography Support.

Getting the Source Code

To clone MimeKit’s source code:

git clone https://github.com/jstedfast/MimeKit.git

To update an existing clone later:

git pull

Building

In the top-level MimeKit directory, you’ll find the following solution file:

• MimeKit.sln - includes the MimeKit.Core and MimeKit.Cryptography projects (targeting .NET Framework 4.6.2/4.7/4.8, .NETStandard 2.0/2.1, .NET 8.0 and .NET 10.0) as well as the unit tests.

Once you’ve opened the MimeKit solution file in Visual Studio, you can choose the Debug or Release build configuration and then build.

Building MimeKit requires the .NET 10.0 SDK (or a version of Visual Studio that includes it). The unit tests target .NET 8.0, so you will also need the .NET 8.0 runtime in order to run them.

You can also build MimeKit from the command line:

dotnet build MimeKit.sln -c Release

Note: The .NET Framework 4.8 target is only built on Windows.

Regenerating the HTML entity decoder

The standalone tools\HtmlEntityDecoderGenerator project generates MimeKit\Text\HtmlEntityDecoder.g.cs from the checked-in UnitTests\TestData\html\HtmlEntities.json snapshot, which is also used by the decoder tests. From the repository root, run:

dotnet run --project tools\HtmlEntityDecoderGenerator

The tool requires the .NET 10.0 SDK and does not download entity data. It preserves the snapshot’s entity order and writes UTF-8 without a BOM, with CRLF line endings. Optional arguments -- <entities.json> [<output.cs>] override the input and output paths. After changing the snapshot, regenerate the decoder and run the UnitTests.Text.HtmlEntityDecoderTests fixture.

Using MimeKit

Parsing Messages

One of the more common operations that MimeKit is meant for is parsing email messages from arbitrary streams. There are two ways of accomplishing this task.

The first way is to use one of the Load methods on MimeMessage:

// Load a MimeMessage from a stream
var message = MimeMessage.Load (stream);

Or you can load a message from a file path:

// Load a MimeMessage from a file path
var message = MimeMessage.Load ("message.eml");

The second way is to use the MimeParser class. For the most part, using the MimeParser directly is not necessary unless you wish to parse a Unix mbox file stream. However, this is how you would do it:

// Load a MimeMessage from a stream
var parser = new MimeParser (stream, MimeFormat.Entity);
var message = parser.ParseMessage ();

For Unix mbox file streams, you would use the parser like this:

// Load every message from a Unix mbox
var parser = new MimeParser (stream, MimeFormat.Mbox);
while (!parser.IsEndOfStream) {
    var message = parser.ParseMessage ();

    // do something with the message
}

Getting the Body of a Message

A common misunderstanding about email is that there is a well-defined message body and then a list of attachments. This is not really the case. The reality is that MIME is a tree structure of content, much like a file system.

Luckily, MIME does define a set of general rules for how mail clients should interpret this tree structure of MIME parts. The Content-Disposition header is meant to provide hints to the receiving client as to which parts are meant to be displayed as part of the message body and which are meant to be interpreted as attachments.

The Content-Disposition header will generally have one of two values: inline or attachment.

The meaning of these values should be fairly obvious. If the value is attachment, then the content of said MIME part is meant to be presented as a file attachment separate from the core message. However, if the value is inline, then the content of that MIME part is meant to be displayed inline within the mail client’s rendering of the core message body. If the Content-Disposition header does not exist, then it should be treated as if the value were inline.

Technically, every part that lacks a Content-Disposition header or that is marked as inline, then, is part of the core message body.

There’s a bit more to it than that, though.

Modern MIME messages will often contain a multipart/alternative MIME container which will generally contain a text/plain and text/html version of the text that the sender wrote. The text/html version is typically formatted much closer to what the sender saw in his or her WYSIWYG editor than the text/plain version.

The reason for sending the message text in both formats is that not all mail clients are capable of displaying HTML.

The receiving client should only display one of the alternative views contained within the multipart/alternative container. Since alternative views are listed in order of least faithful to most faithful with what the sender saw in his or her WYSIWYG editor, the receiving client should walk over the list of alternative views starting at the end and working backwards until it finds a part that it is capable of displaying.

Example:

multipart/alternative
  text/plain
  text/html

As seen in the example above, the text/html part is listed last because it is the most faithful to what the sender saw in his or her WYSIWYG editor when writing the message.

To make matters even more complicated, sometimes modern mail clients will use a multipart/related MIME container instead of a simple text/html part in order to embed images and other content within the HTML.

Example:

multipart/alternative
  text/plain
  multipart/related
    text/html
    image/jpeg
    video/mp4
    image/png

In the example above, one of the alternative views is a multipart/related container which contains an HTML version of the message body that references the sibling video and images.

Now that you have a rough idea of how a message is structured and how to interpret various MIME entities, the next step is learning how to traverse the MIME tree using MimeKit.

Note: For your convenience, MimeKit’s MimeMessage class has two properties that can help you get the text/plain or text/html version of the message body. These are TextBody and HtmlBody, respectively.

Keep in mind, however, that at least with the HtmlBody property, it may be that the HTML part is a child of a multipart/related, allowing it to refer to images and other types of media that are also contained within that multipart/related entity. This property is really only a convenience property and is not a really good substitute for traversing the MIME structure yourself so that you may properly interpret related content.

Converting HTML to Plain Text

Use MimeKit.Text.HtmlToText to turn an HTML document or fragment into readable plain text:

var converter = new MimeKit.Text.HtmlToText {
    OutputLinkUrls = true,
    OutputImageAltText = true
};

string text = converter.Convert ("<h1>Hello</h1><p>Visit <a href=\"https://example.com\">Example</a>.</p>");

The result is:

# Hello

Visit Example (https://example.com).

The converter preserves paragraph breaks, nested lists, blockquotes and preformatted whitespace. It accepts strings, streams or a TextReader/TextWriter pair. Output is not word-wrapped; line endings follow the destination writer’s NewLine property. Headers and footers are literal text, and caller-owned readers, writers and streams remain open.

This is a structural text conversion, not browser rendering or Markdown serialization. CSS and inline emphasis styling are not reproduced; tables are flattened without borders or aligned columns. Script, style, title, template and hidden-element content is omitted, and external resources are never fetched. Link URLs and image alt text are enabled by default and can be disabled independently.

For untrusted input, MaxElementDepth defaults to 4096, MaxInputLength to 16,777,216 UTF-16 characters and MaxOutputLength to 67,108,864 UTF-16 characters. The input limit includes markup and suppressed content; the output limit includes generated indentation, URLs and line endings. The literal header and footer are excluded from these length limits. Exceeding a limit throws FormatException; a streaming destination may already contain partial output.

Converting Enriched Text to HTML

Use MimeKit.Text.EnrichedToHtml to convert RFC 1896 text/enriched content:

var converter = new MimeKit.Text.EnrichedToHtml {
    OutputHtmlFragment = true
};

string html = converter.Convert ("<bold>Hello</bold> <color><param>red</param>world</color>!");

The converter supports emphasis, font families, colors, relative font sizes, alignment, paragraph indentation, excerpts, language tags and nofill. It applies enriched-text newline folding and escapes literal text, including << for a literal less-than sign. Unknown commands are ignored, their body text is retained, and parameter content is never displayed. This does not support the older text/richtext format.

Strings, streams and TextReader/TextWriter pairs are supported. By default the result is wrapped in <html><body>; set OutputHtmlFragment to omit that wrapper. Caller-owned readers, writers and streams remain open. Text headers and footers are converted with TextToHtml; headers and footers explicitly marked as HTML are trusted markup, not sanitized input.

For untrusted input, MaxElementDepth and MaxParameterLength default to 4096, MaxInputLength to 16,777,216 UTF-16 characters and MaxOutputLength to 67,108,864 UTF-16 characters. The input limit includes commands and suppressed parameters, but excludes configured headers and footers. The output limit includes all markup, escaping, headers and footers. Exceeding a limit throws FormatException; a streaming destination may already contain partial output.

Traversing a MimeMessage

The MimeMessage.Body is the top-level MIME entity of the message. Generally, it will either be a TextPart or a Multipart.

As an example, if you wanted to rip out all of the attachments of a message, your code might look something like this:

var attachments = new List<MimePart> ();
var multiparts = new List<Multipart> ();
var iter = new MimeIterator (message);

// collect our list of attachments and their parent multiparts
while (iter.MoveNext ()) {
    var multipart = iter.Parent as Multipart;
    var part = iter.Current as MimePart;

    if (multipart != null && part != null && part.IsAttachment) {
        // keep track of each attachment's parent multipart
        multiparts.Add (multipart);
        attachments.Add (part);
    }
}

// now remove each attachment from its parent multipart...
for (int i = 0; i < attachments.Count; i++)
    multiparts[i].Remove (attachments[i]);

Quick and Dirty Enumeration of Message Body Parts

If you would rather skip the proper way of traversing a MIME tree, another option that MimeKit provides is a simple enumerator over the message’s body parts in a flat (depth-first) list.

You can access this flat list via the BodyParts property, like so:

foreach (var part in message.BodyParts) {
   // do something
}

Another helper property on the MimeMessage class is the Attachments property which works much the same way as the BodyParts property except that it will only contain MIME parts which have a Content-Disposition header value that is set to attachment.

Getting the Decoded Content of a MIME Part

At some point, you’re going to want to extract the decoded content of a MimePart (such as an image) and save it to disk or feed it to a UI control to display it.

Once you’ve found the MimePart object that you’d like to extract the content of, here’s how you can save the decoded content to a file:

// This will get the name of the file as specified by the sending mail client.
// Note: this value *may* be null, so you'll want to handle that case in your code.
var fileName = part.FileName;

using (var stream = File.Create (fileName)) {
    part.Content.DecodeTo (stream);
}

You can also get access to the original raw content by “opening” the Content. This might be useful if you want to pass the content off to a UI control that can do its own loading from a stream.

using (var stream = part.Content.Open ()) {
    // At this point, you can now read from the stream as if it were the original,
    // raw content. Assuming you have an image UI control that could load from a
    // stream, you could do something like this:
    imageControl.Load (stream);
}

There are a number of useful filters that can be applied to a FilteredStream, so if you find this type of interface appealing, I suggest taking a look at the available filters in the MimeKit.IO.Filters namespace or even write your own! The possibilities are limited only by your imagination.

Extracting TNEF (winmail.dat) Attachments

Outlook and Exchange sometimes send messages with an application/ms-tnef attachment, usually named winmail.dat. It holds the message’s real bodies and attachments, packed in Microsoft’s Transport Neutral Encapsulation Format, which most mail clients can’t read. MimeKit parses these attachments as TnefParts.

The easiest way to handle a TnefPart is to convert it to MIME:

foreach (var tnefPart in message.BodyParts.OfType<TnefPart> ()) {
    using (var tnef = tnefPart.LoadTnefMessage ())
    using (var result = tnef.ConvertToMime ()) {
        // result.Message is a regular MimeMessage with the bodies and attachments from the TNEF part.
        // It doesn't depend on the TnefMessage, but it is disposed along with the result.
        foreach (var attachment in result.Message.Attachments.OfType<MimePart> ()) {
            // The file name comes from the sender, so never use it as a path without sanitizing it.
            var fileName = Path.GetFileName (attachment.FileName ?? "attachment.dat");

            using (var stream = File.Create (fileName))
                attachment.Content.DecodeTo (stream);
        }

        // result.Losses lists anything that couldn't be represented in MIME.
    }
}

If you don’t need MIME, TnefMessage exposes the Subject, Recipients, TextBody, HtmlBody, RtfBody, Attachments and raw MAPI Properties directly. TnefMessage.Load (stream) loads a standalone winmail.dat file. TNEF data is untrusted input, so TnefOptions limits nesting depth, attachment count and data sizes.

If you’re porting TNEF code from MimeKit 4.x, see the FAQ and the TNEF section of the Porting Guide.

Checking Messages for MIME Compliance Problems

MimeKit’s parser is very forgiving: it will happily parse messages that violate the MIME specifications in all sorts of ways. Sometimes, though, you’ll want to know about those violations, whether you are debugging a mail client, rejecting malformed messages, or looking for messages that different mail components might interpret differently (a common technique used to smuggle content past spam and malware filters).

To find out, set the ComplianceLogger property of the MimeParser (or MimeReader) to an IMimeComplianceLogger implementation. The parser will then report a MimeComplianceIssue for each problem that it finds, including the type of violation, its severity, its categories (interoperability, data loss and/or security) and where in the stream it was found:

class ConsoleComplianceLogger : IMimeComplianceLogger
{
    public void Log (in MimeComplianceIssue issue)
    {
        Console.WriteLine ("{0}:{1}: {2}: {3} [{4}]", issue.LineNumber, issue.ColumnNumber,
            issue.Severity, issue.Description, issue.Violation);
    }
}

// ...

using (var stream = File.OpenRead ("message.eml")) {
    var parser = new MimeParser (stream) {
        ComplianceLogger = new ConsoleComplianceLogger (),
        ComplianceOptions = new MimeComplianceOptions {
            // Since the issues can be produced by untrusted input, limit how many times each one gets reported.
            MaxIssuesPerViolation = 10
        }
    };

    var message = parser.ParseMessage ();
}

If you only need the compliance report and not the MimeMessage, use a MimeReader instead; it scans the message without building the object tree. For a complete example, see the MimeAnalyzer sample, which reports the issues in a compiler-style file:line:column: severity: message format.

HtmlTokenizer/HtmlToHtml, RtfToText/RtfToHtml and TnefReader have similar ComplianceLogger properties of their own.

Creating a Simple Message

Creating MIME messages using MimeKit is really trivial.

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey", "[email protected]"));
message.To.Add (new MailboxAddress ("Alice", "[email protected]"));
message.Subject = "How you doin?";

message.Body = new TextPart ("plain") {
    Text = @"Hey Alice,

What are you up to this weekend? Monica is throwing one of her parties on
Saturday and I was hoping you could make it.

Will you be my +1?

-- Joey
"
};

A TextPart is a leaf-node MIME part with a text media-type. The first argument to the TextPart constructor specifies the media-subtype, in this case, “plain”. Another media subtype you are probably familiar with is the “html” subtype. Some other examples include “enriched”, “rtf”, and “csv”.

The Text property is the easiest way to both get and set the string content of the MIME part.

Creating a Message with Attachments

Attachments are just like any other MimePart, the only difference is that they typically have a Content-Disposition header with a value of “attachment” instead of “inline” or no Content-Disposition header at all.

Typically, when a mail client adds attachments to a message, it will create a multipart/mixed part and add the text body part and all of the file attachments to the multipart/mixed.

Here’s how you can do that with MimeKit:

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey", "[email protected]"));
message.To.Add (new MailboxAddress ("Alice", "[email protected]"));
message.Subject = "How you doin?";

// create our message text, just like before (except don't set it as the message.Body)
var body = new TextPart ("plain") {
    Text = @"Hey Alice,

What are you up to this weekend? Monica is throwing one of her parties on
Saturday and I was hoping you could make it.

Will you be my +1?

-- Joey
"
};

// create an image attachment for the file located at path
var attachment = new MimePart ("image", "gif") {
    Content = new MimeContent (File.OpenRead (path), ContentEncoding.Unspecified),
    ContentDisposition = new ContentDisposition (ContentDisposition.Attachment),
    ContentTransferEncoding = ContentEncoding.Base64,
    FileName = Path.GetFileName (path)
};

// now create the multipart/mixed container to hold the message text and the
// image attachment
var multipart = new Multipart ("mixed");
multipart.Add (body);
multipart.Add (attachment);

// now set the multipart/mixed as the message body
message.Body = multipart;

Of course, that is just a simple example. A lot of modern mail clients such as Outlook or Thunderbird will send out both a text/html and a text/plain version of the message text. To do this, you’d create a TextPart for the text/plain part and another TextPart for the text/html part and then add them to a multipart/alternative like so:

var attachment = CreateAttachment ();
var plain = CreateTextPlainPart ();
var html = CreateTextHtmlPart ();

// Note: it is important that the text/html part is added second, because it is the
// most expressive version and (probably) the most faithful to the sender's WYSIWYG 
// editor.
var alternative = new Multipart ("alternative");
alternative.Add (plain);
alternative.Add (html);

// now create the multipart/mixed container to hold the multipart/alternative
// and the image attachment
var multipart = new Multipart ("mixed");
multipart.Add (alternative);
multipart.Add (attachment);

// now set the multipart/mixed as the message body
message.Body = multipart;

Creating a Message Using a BodyBuilder (not Arnold Schwarzenegger)

If you are used to System.Net.Mail’s API for creating messages, you will probably find using a BodyBuilder much more friendly than manually creating the tree of MIME parts. Here’s how you could create a message body using a BodyBuilder:

var message = new MimeMessage ();
message.From.Add (new MailboxAddress ("Joey", "[email protected]"));
message.To.Add (new MailboxAddress ("Alice", "[email protected]"));
message.Subject = "How you doin?";

var builder = new BodyBuilder ();

// Set the plain-text version of the message text
builder.TextBody = @"Hey Alice,

What are you up to this weekend? Monica is throwing one of her parties on
Saturday and I was hoping you could make it.

Will you be my +1?

-- Joey
";

// generate a Content-Id for the image we'll be referencing
var contentId = MimeUtils.GenerateMessageId ();

// Set the html version of the message text
builder.HtmlBody = string.Format (@"<p>Hey Alice,<br>
<p>What are you up to this weekend? Monica is throwing one of her parties on
Saturday and I was hoping you could make it.<br>
<p>Will you be my +1?<br>
<p>-- Joey<br>
<center><img src=""cid:{0}"" alt=""selfie.jpg""></center>", contentId);

// Since selfie.jpg is referenced from the html text, we'll need to add it
// to builder.LinkedResources and then set the Content-Id header value
builder.LinkedResources.Add (@"C:\Users\Joey\Documents\Selfies\selfie.jpg");
builder.LinkedResources[0].ContentId = contentId;

// We may also want to attach a calendar event for Monica's party...
builder.Attachments.Add (@"C:\Users\Joey\Documents\party.ics");

// Now we just need to set the message body and we're done
message.Body = builder.ToMessageBody ();

Initializing MimeKit’s Cryptography Support

As of MimeKit 5.0, MimeKit’s S/MIME, PGP/MIME, DKIM, ARC and DMARC support lives in the MimeKit.Cryptography assembly. In order for the parser to create cryptographic MIME entities such as MultipartSigned, MultipartEncrypted and ApplicationPkcs7Mime (instead of a plain Multipart or MimePart), the cryptography module needs to be initialized before any messages are parsed. The best place to do this is during your application’s startup:

using MimeKit.Cryptography;

CryptographyModule.Initialize ();

Note: The cryptography module is also initialized automatically the first time the CryptographyContext class is used (for example, when calling CryptographyContext.Register ()), and it is safe to call CryptographyModule.Initialize () more than once.

Preparing to use MimeKit’s S/MIME support

Before you can begin using MimeKit’s S/MIME support, you will need to decide which S/MIME implementation to use.

If your application runs exclusively on Windows, you’ll probably want to use the WindowsSecureMimeContext backend which is based on the Windows Certificate Store and uses Microsoft’s built-in S/MIME implementation.

On the other hand, if your application or service runs on other platforms such as Linux, macOS, iOS, or Android or is expected to run cross-platform, then you will need to use one of the BouncyCastle-based S/MIME context classes:

• The TemporarySecureMimeContext backend uses an in-memory certificate store and will require your application to load all of the certificates it expects to use into the context before it can be used.
• The DefaultSecureMimeContext backend is designed to use a SQL database for certificate storage such as System.Data.SQLite.

If you opt for using the DefaultSecureMimeContext backend, you’ll need to implement your own DefaultSecureMimeContext subclass. Luckily, it’s very simple to do. Assuming you’ve chosen System.Data.SQLite, here’s how you’d implement your own DefaultSecureMimeContext class:

using System.Data.SQLite;
using MimeKit.Cryptography;

namespace MyAppNamespace {
    class MySecureMimeContext : DefaultSecureMimeContext
    {
        public MySecureMimeContext () : base (OpenDatabase ("C:\\wherever\\certdb.sqlite"))
        {
        }

        static IX509CertificateDatabase OpenDatabase (string fileName)
        {
            var builder = new SQLiteConnectionStringBuilder ();
            builder.DateTimeFormat = SQLiteDateFormats.Ticks;
            builder.DataSource = fileName;

            if (!File.Exists (fileName))
                SQLiteConnection.CreateFile (fileName);

            var sqlite = new SQLiteConnection (builder.ConnectionString);
            sqlite.Open ();

            return new SqliteCertificateDatabase (sqlite, "password");
        }
    }
}

Once you’ve implemented or chosen a suitable SecureMimeContext, you’ll need to register it with MimeKit:

CryptographyContext.Register (typeof (MySecureMimeContext));

Now you are ready to encrypt, decrypt, sign and verify S/MIME messages!

Note: If you choose to use the WindowsSecureMimeContext or TemporarySecureMimeContext backend, you should register that class instead.

Preparing to use MimeKit’s PGP/MIME support

Like with S/MIME support, you also need to register your own OpenPgpContext. Unlike S/MIME, however, you don’t need to choose a database if you subclass GnuPGContext because it uses GnuPG’s PGP keyrings to load and store public and private keys. If you choose to subclass GnuPGContext, the only thing you you need to do is implement a password callback method:

using MimeKit.Cryptography;

namespace MyAppNamespace {
    class MyGnuPGContext : GnuPGContext
    {
        public MyGnuPgContext () : base ()
        {
        }

        protected override string GetPasswordForKey (PgpSecretKey key)
        {
            // prompt the user (or a secure password cache) for the password for the specified secret key.
            return "password";
        }
    }
}

Once again, to register your OpenPgpContext, you can use the following code snippet:

CryptographyContext.Register (typeof (MyGnuPGContext));

Now you are ready to encrypt, decrypt, sign and verify PGP/MIME messages!

Encrypting Messages with S/MIME

S/MIME uses an application/pkcs7-mime MIME part to encapsulate encrypted content (as well as other things).

var joey = new MailboxAddress ("Joey", "[email protected]");
var alice = new MailboxAddress ("Alice", "[email protected]");

var message = new MimeMessage ();
message.From.Add (joey);
message.To.Add (alice);
message.Subject = "How you doin?";

// create our message body (perhaps a multipart/mixed with the message text and some
// image attachments, for example)
var body = CreateMessageBody ();

// now to encrypt our message body using our custom S/MIME cryptography context
using (var ctx = new MySecureMimeContext ()) {
    // Note: this assumes that "Alice" has an S/MIME certificate with an X.509
    // Subject Email identifier that matches her email address. If she doesn't,
    // try using a SecureMailboxAddress which allows you to specify the
    // fingerprint of her certificate to use for lookups.
    message.Body = ApplicationPkcs7Mime.Encrypt (ctx, message.To.Mailboxes, body);
}

Decrypting S/MIME Messages

As mentioned earlier, S/MIME uses an application/pkcs7-mime part with an “smime-type” parameter with a value of “enveloped-data” to encapsulate the encrypted content.

The first thing you must do is find the ApplicationPkcs7Mime part (see the section on traversing MIME parts).

if (entity is ApplicationPkcs7Mime) {
    var pkcs7 = (ApplicationPkcs7Mime) entity;

    if (pkcs7.SecureMimeType == SecureMimeType.EnvelopedData)
        return pkcs7.Decrypt ();
}

Encrypting Messages with PGP/MIME

Unlike S/MIME, PGP/MIME uses multipart/encrypted to encapsulate its encrypted data.

var joey = new MailboxAddress ("Joey", "[email protected]");
var alice = new MailboxAddress ("Alice", "[email protected]");

var message = new MimeMessage ();
message.From.Add (joey);
message.To.Add (alice);
message.Subject = "How you doin?";

// create our message body (perhaps a multipart/mixed with the message text and some
// image attachments, for example)
var body = CreateMessageBody ();

// now to encrypt our message body using our custom PGP/MIME cryptography context
using (var ctx = new MyGnuPGContext ()) {
    // Note: this assumes that "Alice" has a public PGP key that matches her email
    // address. If she doesn't, try using a SecureMailboxAddress which allows you
    // to specify the fingerprint of her public PGP key to use for lookups.
    message.Body = MultipartEncrypted.Encrypt (ctx, message.To.Mailboxes, body);
}

Decrypting PGP/MIME Messages

As mentioned earlier, PGP/MIME uses a multipart/encrypted part to encapsulate the encrypted content.

A multipart/encrypted contains exactly 2 parts: the first MimeEntity is the version information while the second MimeEntity is the actual encrypted content and will typically be an application/octet-stream.

The first thing you must do is find the MultipartEncrypted part (see the section on traversing MIME parts).

if (entity is MultipartEncrypted) {
    var encrypted = (MultipartEncrypted) entity;

    return encrypted.Decrypt ();
}

Digitally Signing Messages with S/MIME or PGP/MIME

Both S/MIME and PGP/MIME use a multipart/signed to contain the signed content and the detached signature data.

Here’s how you might digitally sign a message using S/MIME:

var joey = new MailboxAddress ("Joey", "[email protected]");
var alice = new MailboxAddress ("Alice", "[email protected]");

var message = new MimeMessage ();
message.From.Add (joey);
message.To.Add (alice);
message.Subject = "How you doin?";

// create our message body (perhaps a multipart/mixed with the message text and some
// image attachments, for example)
var body = CreateMessageBody ();

// now to digitally sign our message body using our custom S/MIME cryptography context
using (var ctx = new MySecureMimeContext ()) {
    // Note: this assumes that "Joey" has an S/MIME signing certificate and private key
    // with an X.509 Subject Email identifier that matches Joey's email address.
    message.Body = MultipartSigned.Create (ctx, joey, DigestAlgorithm.Sha1, body);
}

For S/MIME, if you have a way for the user to configure which S/MIME certificate to use as their signing certificate, you could also do something more like this:

// now to digitally sign our message body using our custom S/MIME cryptography context
using (var ctx = new MySecureMimeContext ()) {
    var certificate = GetJoeysX509Certificate ();
    var signer = new CmsSigner (certificate);
    signer.DigestAlgorithm = DigestAlgorithm.Sha1;

    message.Body = MultipartSigned.Create (ctx, signer, body);
}

If you’d prefer to use PGP instead of S/MIME, things work almost exactly the same except that you would use an OpenPGP cryptography context. For example, you might use a subclass of the GnuPGContext that comes with MimeKit if you want to re-use the user’s GnuPG keyrings (you can’t use GnuPGContext directly because it has no way of prompting the user for their passphrase).

For the sake of this example, let’s pretend that you’ve written a minimal subclass of MimeKit.Cryptography.GnuPGContext that only overrides the GetPassword() method and that this subclass is called MyGnuPGContext.

// now to digitally sign our message body using our custom OpenPGP cryptography context
using (var ctx = new MyGnuPGContext ()) {
    // Note: this assumes that "Joey" has a PGP key that matches his email address.
    message.Body = MultipartSigned.Create (ctx, joey, DigestAlgorithm.Sha1, body);
}

Just like S/MIME, however, you can also do your own PGP key lookups instead of relying on email addresses to match up with the user’s private key.

// now to digitally sign our message body using our custom OpenPGP cryptography context
using (var ctx = new MyGnuPGContext ()) {
    var key = GetJoeysPrivatePgpKey ();
    message.Body = MultipartSigned.Create (ctx, key, DigestAlgorithm.Sha1, body);
}

Verifying S/MIME and PGP/MIME Digital Signatures

As mentioned earlier, both S/MIME and PGP/MIME typically use a multipart/signed part to contain the signed content and the detached signature data.

A multipart/signed contains exactly 2 parts: the first MimeEntity is the signed content while the second MimeEntity is the detached signature and, by default, will either be an ApplicationPgpSignature part or an ApplicationPkcs7Signature part (depending on whether the sending client signed using OpenPGP or S/MIME).

Because the multipart/signed part may have been signed by multiple signers, it is important to verify each of the digital signatures (one for each signer) that are returned by the MultipartSigned.Verify() method:

if (entity is MultipartSigned) {
    var signed = (MultipartSigned) entity;

    foreach (var signature in signed.Verify ()) {
        try {
            bool valid = signature.Verify ();

            // If valid is true, then it signifies that the signed content has not been
            // modified since this particular signer signed the content.
            //
            // However, if it is false, then it indicates that the signed content has
            // been modified.
        } catch (DigitalSignatureVerifyException) {
            // There was an error verifying the signature.
        }
    }
}

It should be noted, however, that while most S/MIME clients will use the preferred multipart/signed approach, it is possible that you may encounter an application/pkcs7-mime part with an “smime-type” parameter set to “signed-data”. Luckily, MimeKit can handle this format as well:

if (entity is ApplicationPkcs7Mime) {
    var pkcs7 = (ApplicationPkcs7Mime) entity;

    if (pkcs7.SecureMimeType == SecureMimeType.SignedData) {
        // extract the original content and get a list of signatures
        MimeEntity extracted;

        // Note: if you are rendering the message, you'll want to render the
        // extracted mime part rather than the application/pkcs7-mime part.
        foreach (var signature in pkcs7.Verify (out extracted)) {
            try {
                bool valid = signature.Verify ();

                // If valid is true, then it signifies that the signed content has not
                // been modified since this particular signer signed the content.
                //
                // However, if it is false, then it indicates that the signed content
                // has been modified.
            } catch (DigitalSignatureVerifyException) {
                // There was an error verifying the signature.
            }
        }
    }
}

Signing Messages with DKIM

In addition to OpenPGP and S/MIME, MimeKit also supports DKIM signatures. To sign a message using DKIM, you’ll first need a private key. In the following example, assume that the private key is saved in a file called privatekey.pem:

var headers = new HeaderId[] { HeaderId.From, HeaderId.Subject, HeaderId.Date };
var signer = new DkimSigner ("privatekey.pem", "example.com", "brisbane", DkimSignatureAlgorithm.RsaSha256) {
    HeaderCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Simple,
    BodyCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Simple,
    AgentOrUserIdentifier = "@eng.example.com",
    QueryMethod = "dns/txt",
};

// Prepare the message body to be sent over a 7bit transport (such as older versions of SMTP).
// Note: If the SMTP server you will be sending the message over supports the 8BITMIME extension,
// then you can use `EncodingConstraint.EightBit` instead.
message.Prepare (EncodingConstraint.SevenBit);

signer.Sign (message, headers);

As you can see, it’s fairly straight forward.

Verifying DKIM Signatures

Verifying DKIM signatures is slightly more involved than creating them because you’ll need to write a custom implementation of the IDnsResolver interface. Typically, this custom class will use your chosen DNS library to look up the DNS TXT records requested by MimeKit during verification of DKIM signature headers. MimeKit takes care of parsing the DKIM public key records, so all your resolver needs to do is return the raw TXT record strings along with whether the domain exists or the lookup failed.

Once you’ve implemented a custom IDnsResolver, verifying signatures is fairly trivial. Most of the work needed will be in the IDnsResolver implementation. As an example of how to implement this interface, here is one possible implementation using the DnsClient library:

using System;
using System.IO;
using System.Net;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Concurrent;

using DnsClient;

using MimeKit;
using MimeKit.Cryptography;

namespace DkimVerifierExample
{
    class DnsResolver : IDnsResolver
    {
        readonly ConcurrentDictionary<string, DnsTxtResponse> cache;
        readonly LookupClient dnsClient;

        public DnsResolver ()
        {
            cache = new ConcurrentDictionary<string, DnsTxtResponse> (StringComparer.OrdinalIgnoreCase);

            var options = new LookupClientOptions (IPAddress.Parse ("8.8.8.8")) {
                UseCache = true,
                Retries = 3
            };

            dnsClient = new LookupClient (options);
        }

        DnsTxtResponse GetTxtResponse (string domain, IDnsQueryResponse response)
        {
            DnsTxtResponse result;

            if (response.HasError) {
                if (response.Header.ResponseCode == DnsHeaderResponseCode.NotExistentDomain)
                    result = new DnsTxtResponse (DnsQueryStatus.NonExistentDomain);
                else
                    return new DnsTxtResponse (DnsQueryStatus.TemporaryFailure);
            } else {
                // Each TXT record may be split into multiple character-strings which must be concatenated.
                // Note: separate TXT records must *not* be concatenated together.
                var records = response.Answers.TxtRecords ().Select (record => string.Concat (record.Text));

                result = new DnsTxtResponse (records);
            }

            // only cache definitive answers
            cache[domain] = result;

            return result;
        }

        public DnsTxtResponse QueryTxt (string domain, CancellationToken cancellationToken = default)
        {
            // check if we've already fetched this record
            if (cache.TryGetValue (domain, out var cached))
                return cached;

            try {
                var response = dnsClient.Query (domain, QueryType.TXT, QueryClass.IN);

                return GetTxtResponse (domain, response);
            } catch (DnsResponseException) {
                return new DnsTxtResponse (DnsQueryStatus.TemporaryFailure);
            }
        }

        public async Task<DnsTxtResponse> QueryTxtAsync (string domain, CancellationToken cancellationToken = default)
        {
            // check if we've already fetched this record
            if (cache.TryGetValue (domain, out var cached))
                return cached;

            try {
                var response = await dnsClient.QueryAsync (domain, QueryType.TXT, QueryClass.IN, cancellationToken).ConfigureAwait (false);

                return GetTxtResponse (domain, response);
            } catch (DnsResponseException) {
                return new DnsTxtResponse (DnsQueryStatus.TemporaryFailure);
            }
        }
    }

    class Program
    {
        public static void Main (string[] args)
        {
            if (args.Length == 0) {
                Help ();
                return;
            }

            for (int i = 0; i < args.Length; i++) {
                if (args[i] == "--help") {
                    Help ();
                    return;
                }
            }

            var resolver = new DnsResolver ();
            var verifier = new DkimVerifier (resolver);

            for (int i = 0; i < args.Length; i++) {
                if (!File.Exists (args[i])) {
                    Console.Error.WriteLine ("{0}: No such file.", args[i]);
                    continue;
                }

                Console.Write ("{0} -> ", args[i]);

                var message = MimeMessage.Load (args[i]);
                // verify each of the DKIM-Signature headers (up to verifier.MaxSignatures)
                var results = verifier.Verify (message);

                if (results.Length == 0) {
                    Console.WriteLine ("NO SIGNATURE");
                    continue;
                }

                Console.WriteLine ();

                foreach (var result in results) {
                    Console.Write ("  d={0}; s={1} -> ", result.Domain, result.Selector);

                    if (result.Status == DkimSignatureStatus.Pass) {
                        // the DKIM-Signature header is valid!
                        Console.ForegroundColor = ConsoleColor.Green;
                        Console.WriteLine ("PASS");
                    } else {
                        // the DKIM-Signature header is invalid (Fail), uses a disallowed algorithm or key (Policy),
                        // could not be verified due to a DNS error (TempError) or is malformed (PermError).
                        Console.ForegroundColor = ConsoleColor.Red;
                        Console.WriteLine ("{0} ({1})", result.Status.ToString ().ToUpperInvariant (), result.Reason);
                    }

                    Console.ResetColor ();


提示：代码过长已自动截断

Signing Messages with ARC

Signing with ARC is similar to DKIM but quite a bit more involved. In order to sign with ARC, you must first validate that the existing message is authentictic and produce an ARC-Authentication-Results header containing the methods that you used to authenticate the message as well as their results.

The abstract ArcSigner class provided by MimeKit will need to be subclassed before it can be used. An example subclass that provides 2 different implementations for generating the ARC-Authentication-Results header can be seen below:

using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;

using MimeKit;
using MimeKit.Cryptography;

namespace ArcSignerExample
{
    class MyArcSigner : ArcSigner
    {
        public MyArcSigner (string fileName, string domain, string selector, DkimSigningAlgorithm algorithm = DkimSignatureAlgorithm.RsaSha256)
               : base (fileName, domain, selector, algorithm)
        {
        }

        /// <summary>
        /// Generate the ARC-Authentication-Results header.
        /// </summary>
        /// <remarks>
        /// The ARC-Authentication-Results header contains information detailing the results of
        /// authenticating/verifying the message via ARC, DKIM, SPF, etc.
        ///
        /// In the following implementation, we assume that all of these authentication results
        /// have already been determined by other mail software that has added some Authentication-Results
        /// headers containing this information.
        ///
        /// Note: This method is used when ArcSigner.Sign() is called instead of ArcSigner.SignAsync().
        /// </remarks>
        protected override AuthenticationResults GenerateArcAuthenticationResults (FormatOptions options, MimeMessage message, CancellationToken cancellationToken)
        {
            const string AuthenticationServiceIdentifier = "lists.example.com";

            var results = new AuthenticationResults (AuthenticationServiceIdentifier);

            for (int i = 0; i < message.Headers.Count; i++) {
                var header = message.Headers[i];

                if (header.Id != HeaderId.AuthenticationResults)
                    continue;

                if (!AuthenticationResults.TryParse (header.RawValue, out AuthenticationResults authres))
                    continue;

                if (authres.AuthenticationServiceIdentifier != AuthenticationServiceIdentifier)
                    continue;

                // Merge any authentication results that aren't already known.
                foreach (var result in authres.Results) {
                    if (!results.Results.Any (r => r.Method == result.Method))
                        results.Results.Add (result);
                }
            }

            return results;
        }

        /// <summary>
        /// Generate the ARC-Authentication-Results asynchronously.
        /// </summary>
        /// <remarks>
        /// The ARC-Authentication-Results header contains information detailing the results of
        /// authenticating/verifying the message via ARC, DKIM, SPF, etc.
        ///
        /// In the following implementation, we assume that we have to verify all of the various
        /// authentication methods ourselves.
        ///
        /// Note: This method is used when ArcSigner.SignAsync() is called instead of ArcSigner.Sign().
        /// </remarks>
        protected override async Task<AuthenticationResults> GenerateArcAuthenticationResultsAsync (FormatOptions options, MimeMessage message, CancellationToken cancellationToken)
        {
            const string AuthenticationServiceIdentifier = "lists.example.com";

            var results = new AuthenticationResults (AuthenticationServiceIdentifier);
            var resolver = new DnsResolver (); // from the DKIM example above
            var dkimVerifier = new DkimVerifier (resolver);
            var arcVerifier = new ArcVerifier (resolver);
            AuthenticationMethodResult method;

            // Add the ARC authentication results
            var arc = await arcVerifier.VerifyAsync (message, cancellationToken);

            // Note: As required by RFC 8617, any failure to validate the ARC chain (including DNS failures)
            // results in a "fail". If the failure was due to a temporary DNS failure, you may prefer to
            // temporarily reject (defer) the message and try again later rather than sealing it with cv=fail.
            if ((arc.ChainErrors & ArcValidationErrors.DnsTemporaryFailure) != 0)
                throw new TimeoutException ("Temporary DNS failure while validating the ARC chain.");

            method = new AuthenticationMethodResult ("arc", arc.Chain.ToString ().ToLowerInvariant ());
            results.Results.Add (method);

            // Add authentication results for each DKIM signature
            // (the dkim method results include the header.d, header.i, header.s, header.a and header.b properties)
            foreach (var dkim in await dkimVerifier.VerifyAsync (message, cancellationToken))
                results.Results.Add (dkim.ToAuthenticationMethodResult ());

            return results;
        }
    }
}

Once you have a custom ArcSigner class, the actual logic for signing is almost identical to DKIM.

Note: As with the DKIM signing example above, assume that the private key is saved in a file called privatekey.pem:

var headers = new HeaderId[] { HeaderId.From, HeaderId.Subject, HeaderId.Date };
var signer = new MyArcSigner ("privatekey.pem", "example.com", "brisbane", DkimSignatureAlgorithm.RsaSha256) {
    HeaderCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Relaxed,
    BodyCanonicalizationAlgorithm = DkimCanonicalizationAlgorithm.Relaxed,
    AgentOrUserIdentifier = "@eng.example.com"
};

// Prepare the message body to be sent over a 7bit transport (such as older versions of SMTP).
// Note: If the SMTP server you will be sending the message over supports the 8BITMIME extension,
// then you can use `EncodingConstraint.EightBit` instead.
message.Prepare (EncodingConstraint.SevenBit);

signer.Sign (message, headers); // or SignAsync

Verifying ARC Signatures

Just like with verifying DKIM signatures, you will need to implement the IDnsResolver interface. To see an example of how to implement this interface, see the DKIM signature verification example above.

The ArcVerifier works exactly the same as the DkimVerifier except that it is not necessary to provide a Header argument to the Verify or VerifyAsync method.

var verifier = new ArcVerifier (new DnsResolver ());
var results = await verifier.VerifyAsync (message);

// The Chain results are the only real important results.
Console.WriteLine ("ARC results: {0}", results.Chain);

// As required by RFC 8617, any validation error (including DNS failures) results in a Fail.
// The ChainErrors and the Reason/Exception properties of each header result provide diagnostics.
if ((results.ChainErrors & ArcValidationErrors.DnsTemporaryFailure) != 0)
    Console.WriteLine ("The ARC chain could not be validated due to a temporary DNS failure; try again later.");

if (results.MessageSignature?.Reason != null)
    Console.WriteLine ("ARC-Message-Signature: {0}", results.MessageSignature.Reason);

Verifying DMARC

The DmarcVerifier determines whether a message’s author domain (the domain in the From header) was authenticated by an aligned DKIM signature or SPF check, and which policy the domain owner has requested for messages that fail. It uses the same IDnsResolver interface as the DkimVerifier to discover the DMARC policy and determine Organizational Domains, so no Public Suffix List is needed.

MimeKit does not implement SPF, so you will need to supply the result of your own SPF check of the MAIL FROM (or HELO) domain. If you have not already verified the DKIM signatures, the DmarcVerifier will do it for you using its DkimVerifier property.

var resolver = new DnsResolver (); // from the DKIM example above
var verifier = new DmarcVerifier (resolver);

// The result of an SPF check performed by your SMTP server or a third-party SPF library.
var spf = new SpfCheckResult (SpfStatus.Pass, "bounces.example.com");

var result = await verifier.VerifyAsync (message, spf);

Console.WriteLine ("DMARC result for {0}: {1}", result.AuthorDomain, result.Status);

switch (result.Status) {
case DmarcStatus.Pass:
    // An aligned DKIM signature (result.AlignedDkimResult) or SPF result passed.
    break;
case DmarcStatus.Fail:
    // result.Policy is the policy requested by the domain owner (already adjusted for the
    // sp=, np= and t= tags): None, Quarantine or Reject. The final decision is up to you.
    Console.WriteLine ("Requested policy: {0}", result.Policy);
    break;
case DmarcStatus.TempError:
    // A DNS failure or a DKIM/SPF temporary error prevented a definitive result; try again later.
    break;
case DmarcStatus.PermError:
    // The message has no From header, multiple From headers, or no usable author domain.
    break;
case DmarcStatus.None:
    // The author domain does not publish a DMARC policy.
    break;
}

// result.Errors provides additional diagnostics, and the result can be added to an
// Authentication-Results header using result.ToAuthenticationMethodResult ().

If you have already verified the DKIM signatures, you can pass those results to the DmarcVerifier to avoid verifying them twice:

var dkimResults = await verifier.DkimVerifier.VerifyAsync (message);
var result = await verifier.VerifyAsync (message, dkimResults, spf);

Contributing

The first thing you’ll need to do is fork MimeKit to your own GitHub repository. For instructions on how to clone it, see the section titled Getting the Source Code.

If you use [

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