The "pro" is a substantial re-write. I threw out code that I do not own (like the NTLM authentication) or that wasn't used (rfc822 parsing), fixed some stuff (O

The "pro" is a substantial re-write. I threw out code that I do not own (like the NTLM authentication) or that wasn't used (rfc822 parsing), fixed some stuff (OAuth), rewrote some parts (DKIM), added some new features (DSN), started using ES6 syntax in the entire codebase and bundled all previously separated modules into a single one which means that installation from npm should take less than 2 seconds.