System.Security.Cryptography vs Org.BouncyCastle.Crypto about mimekit

[jstedfast]

I didn't abandon the code for simply performance reasons. I abandoned it (for now) because I didn't have a way to fully support DKIM using System.Security due to the use of unsupported crypto algorithms, namely ED25519.

Unfortunately, even once dotnet adds support for it, I won't be able to switch to System.Security's implementation because it won't be supported on all versions of .NET/.NET Framework.

My hope when I implemented the non-BouncyCastle code-paths was to add DKIM support to MimeKitLite, but shortly after starting to implement it, I had to add support for ED25519 and that pretty much killed my efforts.

At that point, the only reason to keep it around was maybe perf reasons but as I noted, there wasn't any noticeable perf difference, so it became pointless.