Sourced from MimeKit's changelog.

MimeKit 3.1.0 (2022-01-14)

• Always use a lowercase domain name in the Message-Id to work around bugs in eM Client. (issue #734)
• Improved handling of parsing Content-Types like "multipart/multipart/mixed; boundary=...". (issue #737)
• Added a maxLineLength argument to the QuotedPrintableEncoder .ctor.
• Added maxLineLength arguments to EncoderFilter.Create() methods.
• Fixed MimePart.Prepare() to remember the maxLineLength argument value for later use in the WriteTo() implementation. This maxLineLength value can then be passed to the Base64 or QuotedPrintable encoder so that it can properly limit lines to that length (up to a max of 76 characters as per the specs). (issue #743)
• Added net6.0 to the list of TargetFrameworks.

MimeKit 3.0.0 (2021-12-11)

• Removed APIs marked as [Obsolete] in 2.x.
• Refactored X509CertificateDatabase protected methods to include a DbConnection parameter.
• Removed OpenPgpContextBase by folding the logic into OpenPgpContext.
• Added Async APIs for OpenPGP and S/MIME.
• Lazy-load headers on MimeMessage and MimeEntity (and subclasses) to improve performance.
• Added a new MimeReader class that acts as a lower-level MimeParser alternative, allowing developers to parse MIME content without having to instantiate a MIME tree of objects or wait until the parser has completed (and returned a MimeMessage or MimeEntity object) before processing MIME data. This is conceptually similar to a SAX XML parser approach.
• Added a new ExperimentalMimeParser that duplicates MimeParser functionality, but is built on top of MimeReader. This implementation will eventually replace MimeParser once I get some feedback on it. Should be ~5% faster than MimeParser.
• Improved MimeParser performance slightly based on some of the experimentation done to make the ExperimentalMimeParser fast.
• Added CancellationToken arguments for some AttachmentCollection.Add() overloads.
• Use 'net5.0' as the .NET 5.0 target framework moniker instead of 'net50'. (issue #720)
• Drop support for .NET 4.5 and replace it with .NET 4.5.2
• Bumped Portable.BouncyCastle to 1.9.0
• Added new MimeMessage.GetRecipients() method.
• Make it possible to bypass MimeEntity preparation for signing by adding a PrepareBeforeSigning property to CryptographyContext. (issue #721)
• MimeMessage and MimeEntity now implement IDisposable. (issue #732)

• 3a96a26 Bumped version to 3.1.0
• a084f19 Update main.yml
• 229c570 Build MimeKit and MimeKitLite for net6.0 as well
• 696bb35 Remember the maxLineLength passed to the MimePart.Prepare() method
• 523f7e8 Added maxLineLength arguments to EncoderFilter.Create() methods
• 7826fd5 Snap the maxLineLength argument for Base64/QuotedPrintable encoders to 76
• 6833815 Added a maxLineLength argument to the QuotedPrintableEncoder .ctor
• 3ce7c70 Use Windows-style backslashes
• 9a14604 Updated coveralls.ps1
• 98d0b39 Parse NUnit.ConsoleRunner version info from UnitTests.csproj
• Additional commits viewable in compare view

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot merge will merge this PR after your CI passes on it
• @dependabot squash and merge will squash and merge this PR after your CI passes on it
• @dependabot cancel merge will cancel a previously requested merge and block automerging
• @dependabot reopen will reopen this PR if it is closed
• @dependabot close will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)