Re: New issue (was Re: rfc2821bis-01 Issue 18: Usability of 1yz replies

David F. Skoll writes:
> (I'm not too sure what to do if an undefined code is received in 
> response to a RCPT command. It's clear to me that you don't want to 
> continue the SMTP transaction, but do you want to fail all the 
> recipients and generate a non-delivery notification?
The latter. Absolutely. The response is of a kind the client doesn't 
know, so it has absolutely no basis for assuming that the error relates 
only to this client.
Falling back to the next MX is vastly better than assuming anything 
about a 7xx response.
Arnt