MailKit
MimeKit is a robust and high-performance .NET MIME parser, capable of parsing gigabytes of mail in seconds. It offers full support for S/MIME, OpenPGP, DKIM, and ARC signatures, ensuring top-notch security. As an open-source project, it's free for commercial use and runs on multiple platforms including Windows, Linux, Mac, iOS, Android, and Windows Phone. MimeKit, along with MailKit, is designed to be easy to use with comprehensive documentation and community support available through Stack Overflow and GitHub.
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