MimeKit

| Package |Latest Release|Latest Build| |:----------|:------------:|:----------:| |MimeKit||| |MimeKitLite||| |MailKit||| |MailKitLite|||

| Platform |Build Status|Code Coverage|Static Analysis| |:-------------|:----------:|:-----------:|:-------------:| |Linux/Mac|||| |Windows ||||

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.

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.

<a href="https://github.com/sponsors/jstedfast" _target="blank"><img alt="Click here to lend your support to MimeKit by making a donation!" src="https://www.paypal.com/en_US/i/btn/x-click-but21.gif"></a>

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

While mainstream beliefs may suggest that C# can never be as fast as C, it turns out that with a bit of creative parser design and a few clever optimizations ^{[1] [2]}, MimeKit's performance is actually on par with GMime.

Since GMime is pretty well-known as a high-performance native MIME parser and MimeKit more-or-less matches GMime's performance, it stands to reason that MimeKit is likely unsurpassed in performance in the .NET MIME parser space.

For a comparison, as I blogged here (I have since optimized MimeKit by at least another 30%), MimeKit is more than 25x faster than OpenPOP.NET, 75x faster than SharpMimeTools, and 65x faster than regex-based parsers. Even the commercial MIME parser offerings such as LimiLabs' Mail.dll and NewtonIdeas' Mime4Net cannot even come close to matching MimeKit's performance (they are both orders of magnitude slower than MimeKit).

For comparison purposes, I've published a MIME parser benchmark to make it easier for anyone else to compare the performance of MimeKit to their favourite MIME parser.

Here are the results:

Parsing startrek.msg (1000 iterations):
MimeKit:        0.6989221 seconds
OpenPop:        25.3056064 seconds
AE.Net.Mail:    17.5971438 seconds
MailSystem.NET: 26.3891218 seconds
MIMER:          76.4538978 seconds

Parsing xamarin3.msg (1000 iterations):
MimeKit:        3.4215505 seconds
OpenPop:        159.3308053 seconds
AE.Net.Mail:    132.3044291 seconds
MailSystem.NET: 133.5832078 seconds
MIMER:          784.433441 seconds

How does your MIME parser compare?

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.

In Visual Studio's Package Manager Console, enter the following command:

Install-Package MimeKit

Getting the Source Code

First, you'll need to clone MimeKit from my GitHub repository. To do this using the command-line version of Git, you'll need to issue the following command in your terminal:

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

If you are using TortoiseGit on Windows, you'll need to right-click in the directory where you'd like to clone MimeKit and select Git Clone... in the menu. Once you do that, you'll get the following dialog:

Fill in the areas outlined in red and then click OK. This will recursively clone MimeKit onto your local machine.

Updating the Source Code

Occasionally you might want to update your local copy of the source code if I have made changes to MimeKit since you downloaded the source code in the step above. To do this using the command-line version fo Git, you'll need to issue the following commands in your terminal within the MimeKit directory:

git pull
git submodule update

If you are using TortoiseGit on Windows, you'll need to right-click on the MimeKit directory and select Git Sync... in the menu. Once you do that, you'll need to click the Pull and Submodule Update buttons in the following dialog:

Building

In the top-level MimeKit directory, there are a number of solution files; they are:

• MimeKit.sln - includes projects for .NET Framework 4.6.2/4.7/4.8, .NETStandard 2.0/2.1, .NET 6.0 as well as the unit tests.
• MimeKitLite.sln - includes projects for the stripped-down versions of MimeKit that drop support for crypto.

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

Both Visual Studio 2022 and Visual Studio 2019 should be able to build MimeKit without any issues, but older versions such as Visual