Send 550 in response to SMTP RCPT

[Mortal]

"Real" SMTP servers often reply with 550 in response to the RCPT command, so that the SMTP client doesn't have to send message data for a recipient that doesn't exist on the server. Would it be possible to add a hook in aiosmtpd.smtp.SMTP.smtp_DATA to validate incoming recipients immediately instead of just adding them blindly to envelope.rcpt_tos?

I've been running an SMTP mailing list forwarder based on smtpd for two years and am looking into porting that to aiosmtpd when 1.0 is released.

[warsaw]

I think this will be handled with #41

The idea is that the handler would determine whether the recipient is valid or not (via the handler.handle_RCPT hook). Some of the details of that PR still need to be worked out, e.g. the method names need to be updated, but do take a look and see if the general approach will let you do what you need to do.

We will definitely get 1.0 out in the next couple of weeks. I am presenting aiosmtpd at Pycon 2017, so it better be ready by then. :)

[Mortal]

I hadn't noticed PR #41. As far as I can see, the patch doesn't do what I want: SMTP.smtp_RCPT still unconditionally responds 250 OK. I would like event_handler.rcpt to be able to reject the recipient with either a 4xx transient error or 5xx permanent error (most of the time, 550 no such user).

Should we continue the discussion here or in #41?

I'm looking forward to the last-minute 1.0 release on May 21. :-)

[warsaw]

@Mortal I think you've identified a good point. rcpt (to be called handle_RCPT) should not return an address object, but instead it should return a code, or otherwise cause a code to percolate up to smtp_RCPT().

Yes, let's continue the discussion over in #41 - and I sure hope to get 1.0 out way before then! :)

[Mortal]

Implemented in #55.