On 2 Nov 2016, at 7:28, Karel wrote:
On 2016-11-02 11:36, Wietse Venema wrote:
NOQUEUE: reject: RCPT from unknown[x.x.x.x]: 450 4.7.1 Client host
rejected: cannot find your hostname, [x.x.x.x]
Note that this is a 450 status, because the name server did not
reply.
A proper SMTP client will therefore try to deliver the email later.
but looking in my logs, I see also 450 status when nameserver is
reachable, but hostname could not be resolved (because it does not
exist)
In other words, from the logs I cannot tell the difference whether
nameserver was offline, or IP simply does not resolve.
From the man page for postconf(5):
unknown_client_reject_code (default: 450)
The numerical Postfix SMTP server response code when a
client
without valid address <=> name mapping is rejected by
the
reject_unknown_client_hostname restriction. The SMTP
server
always replies with 450 when the mapping failed due to a
tempo-
rary error condition.
Do not change this unless you have a complete understanding
of
RFC 5321.
You can change unknown_client_reject_code to 550 if you want to
permanently reject when you get a hard DNS resolution failure. If you
only want to change the code for better log differentiation, 451 or 455
would be arguably not wrong alternatives to 450.
