Hi there,

We have an IIS SMTP server which sends out a largish number of mails (4000 or so) in batches overnight, and recently we've seen mails get "stuck" in the queue directory. Normally restarting the SMTP service seems to fix this, but it's happened a few times so I'm looking for more information.

We sent out around 12,000 emails last night in 3 batches of roughly 4000. Around 10 hours later there are still 2000 or so in the queue directory which don't seem to be leaving the queue.

Any new mails which appear in the queue are picked up almost immediately and sent to their destination, but these 2000 or so don't seem to move.

Looking at the date modified on the emails some match up with the time they were sent, but around 1000 of them have modified dates stretching up to now. e.g. there was one mail with a date in the message headers of 5:30 this morning, but it's date modified is 11:50 and there are 3 other messages with a date modified of 11:50, then 5 with 11:49, 2 with 11:45 stretching back for a few hours and all with actual message headers far earlier.

The logs for the server look like this

11:54:52 127.0.0.1 EHLO - 250
11:54:52 127.0.0.1 MAIL - 250
11:54:52 127.0.0.1 RCPT - 250
11:54:52 127.0.0.1 DATA - 250
11:54:52 127.0.0.1 QUIT - 240
11:54:53 85.115.62.190 - - 0
11:54:53 85.115.62.190 EHLO - 0
11:54:53 85.115.62.190 - - 0
11:54:53 85.115.62.190 MAIL - 0
11:54:53 85.115.62.190 - - 0
11:54:53 85.115.62.190 RCPT - 0
11:54:53 85.115.62.190 - - 0
11:54:53 85.115.62.190 DATA - 0
11:54:53 85.115.62.190 - - 0
11:54:54 85.115.62.190 - - 0
11:54:54 85.115.62.190 QUIT - 0
11:54:54 85.115.62.190 - - 0

All codes are either 250 or 240 or 0. I believe 250 and 240 indicate success, but I don't know what all the 0s are.

Could someone with more experience of mail server troubleshooting give me a hand or tell me what to try next.

Thanks,

Tom