[enhancement]: create SMTP server trait

[Tobias Florek]

Which feature or improvement would you like to request?

I'd like to see this feature:

I want to programmatically process incoming mail but like to use a hardened and tested library for the SMTP handshake and StartTLS part.

Ideally I would only implement a trait that can respond to ehlo, rcpt and (an abstraction of) data.

Is your feature request related to a problem?

No response

Code of Conduct

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[Tobias Florek]

Also, I forgot auth.