John Levine:
> RFC 5321 says that if a mail server gives an initial banner with a 554
> status code, that means "no mail server here", so the client should do
> whatever it normally does on a connection failure, looking for another
> MX at equal or lower priority.
I don't think that Postfix has ever distinguished between 5xx codes
at this protocol stage. The documentation says:
smtp_skip_5xx_greeting (default: yes)
Skip remote SMTP servers that greet with a 5XX status code
(go away, do not try again later).
By default, the Postfix SMTP client moves on the next mail
exchanger. Specify "smtp_skip_5xx_greeting = no" if Postfix
should bounce the mail immediately. The default setting is
incorrect, but it is what a lot of people expect to happen.
The Postfix documentation is based on RFC 821, which defines "220"
and "421" as "connection establishment" reply codes. The 554 reply
code was introduced with RFC 2821, and I must have missed that.
The default Postfix setting provides the behavior that RFC 2821 and
later want to see. So it looks like Postfix is good to go.
I will update the Postfix documentation.
Wietse
