TODO

DKIM
- It would be nice to make DKIM support not depend on BouncyCastle at all so that DKIM support could be added to MimeKitLite. See: #296 (comment)
- If we had a nice DNS library that supported async/await, we could drop the IDkimPublicKeyLocator interface or at least provide a default implementation. Is it time for me to write DnsKit??
S/MIME
- BouncyCastleSecureMimeContext
  - Add support for downloading CRLs via FTP? Is this needed or at all common?
- Add a RECORDVERSION table column to the SQL database so we can add columns in the future and work around gaps in the row data?

Pie-in-the-sky Ideas