sendmail issue ... stat=Service unavailable

socalheel · 06-04-2014, 11:31 AM

i am seeing quite a bit stat=Service unavailable errors in my maillog and i am not sure why.

initially there is the stat=Service unavailable error, then a few hours later i will see the message was sent=OK.

the only commonality is that the from email addresses are from aol and/or yahoo. i have a feeling this is why the error Service unavailable is occurring then it successfully sends later, but i cannot prove it.

anyone have some idea/input that could be beneficial to help figuring this out?

here is an example:

Code:

May  4 13:58:06 smtp01 sendmail[23609]: s44Hw6dl023609: from=<userone@yahoo.com>, size=5168, class=0, nrcpts=2, msgid=<201405041758.s44Hw6dl023609@smtp01.work.com>, proto=ESMTP, daemon=MTA, relay=ec2-1-1-1-1.compute-1.amazonaws.com [1.1.1.1]

May  4 13:58:06 smtp01 sendmail[23613]: s44Hw6dl023609: to=<admin@customer.com>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=155168, relay=aspmx.l.google.com. [173.194.68.27], dsn=5.0.0, stat=Service unavailable

May  4 13:58:06 smtp01 sendmail[23613]: s44Hw6dl023609: s44Hw6dk023613: DSN: Service unavailable

Code:

May 17 00:44:47 smtp01 sendmail[19983]: s4H4ikof019983: from=<user@aol.com>, size=5319, class=0, nrcpts=2, msgid=<201405170444.s4H4ikof019983@smtp01.work.com>, proto=ESMTP, daemon=MTA, relay=ec2-1-1-1-1.compute-1.amazonaws.com [54.83.2.55]

May 17 00:44:47 smtp01 sendmail[19987]: s4H4ikof019983: to=<admin@customer.com>, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=155319, relay=aspmx.l.google.com. [173.194.76.27], dsn=5.0.0, stat=Service unavailable

May 17 00:44:47 smtp01 sendmail[19987]: s4H4ikof019983: s4H4iloe019987: DSN: Service unavailable

smallpond · 06-04-2014, 01:12 PM

It's called greylisting.

socalheel · 06-04-2014, 03:48 PM

i am familiar with greylisting but to my understanding, greylisting is simply a delay from the receiving server because it does not recognize that domain. but why would it be greylisted well after six weeks of mail being delivered to the same account from the same domain and/or ip address?

at what point does my server qualify as being recognized and no longer greylisted?

RandomTroll · 06-05-2014, 06:13 PM

The parameters of greylisting are up to the recipient server. The one I set up had 2 principal times, one the time a sender had to wait before re-trying, the other the time a sender stayed on the non-greylist between messages. I could have made them anything I wanted; the former was usually in minutes, the latter usually in weeks.

Our greylister replied with the time the sender had to wait before re-sending (counting on spammers either to have reported an invalid address or not bothering to read replies), which I don't see in your log.