MimeKit is an Open Source library for creating and parsing MIME, S/MIME and PGP messages on desktop and mobile platforms. It also supports parsing of Unix mbox files.

  Unlike any other .NET MIME parser, MimeKit's parser does not need to parse string input nor does it use a TextReader. Instead, it parses raw byte streams, thus allowing it to better support undeclared 8bit text in headers as well as message bodies. It also means that MimeKit's parser is significantly faster than other .NET MIME parsers.

  MimeKit's parser also uses a real tokenizer when parsing the headers rather than regex or string.Split() like most other .NET MIME parsers. This means that MimeKit is much more RFC-compliant than any other .NET MIME parser out there, including the commercial implementations.

  In addition to having a far superior parser implementation, MimeKit's object tree is not a derivative of System.Net.Mail objects and thus does not suffer from System.Net.Mail's limitations.

  API documentation can be found on the web at http://www.mimekit.net/docs

  For those that need SMTP, POP3 or IMAP support, check out https://github.com/jstedfast/MailKit

<PackageReference Include="MimeKit" Version="4.18.0.2174" />

source https://www.myget.org/F/mimekit/api/v3/index.json

nuget MimeKit  ~> 4.18.0.2174

Import-Module PowerShellGet
Register-PSRepository -Name "mimekit" -SourceLocation "https://www.myget.org/F/mimekit/api/v2"
Install-Module -Name "MimeKit" -RequiredVersion "4.18.0.2174" -Repository "mimekit" 

Org.BouncyCastle.Utilities.Properties.SetThreadBoolean (Org.BouncyCastle.Utilities.Properties.CmsAllowLenientRsaPkcs1, true);