Getting 2 replies means SMTP PIPELINING is used, and "DATA" is sent before reply to "RCPT TO". 451 is a reply for 'RCPT TO' to and 503 is a reply to DATA. qwest.net announce PIPELINING in EHLO, so it's OK. In this case, 451 should be used. 451 is probably result of graylisting and receiver expects retry with the same MX server after some time. If sender acts as if 503 received, it's a bug, you can try to disable pipelining to fix it.
If sender goes to secondary MX and receives 554 for "RCPT TO", it's probably valid behavior, but is less expected one, usually one expects sender to retry primary MX after some time. RFC is not clear for this case. So it can be misconfiguration (with either graylisting or secondary MX), or may be you are really on the graylist+blacklist. 07.11.2017 4:09, [email protected] пишет: > One of my users is seeing repeated fails to send to hosted mail for nsf.gov > from qwest.net: > > first MX: > >>>>> ... while talking to stn-mtpe-01-03-p.inet.qwest.net.: >>>>>>>> DATA >>>>> <<< 451 4.3.2 Please try again later >>>>> <[email protected]>... Deferred: 451 4.3.2 Please try again later >>>>> <<< 503 5.0.0 Need RCPT (recipient) > second MX: > >>>>> ... while talking to cec-mtpe-01-03-p.inet.qwest.net.: >>>>>>>> DATA >>>>> <<< 554 5.7.1 Access denied >>>>> 554 5.0.0 Service unavailable >>>>> <<< 503 5.0.0 Need RCPT (recipient) > Between the first MX sending back two conflicting replies to one DATA, > and the second one apparently not accepting mail that it should, it looks like > there's multiple places needing some percussive maintenance.... > > > _______________________________________________ > mailop mailing list > [email protected] > https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop -- Vladimir Dubrovin @Mail.Ru
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