Exchg2003 SBS with latest Service Packs, and the Intelligent Message Filter enabled.Server was refusing to accept emails from certain people and/or domains.If I sent an email from home via my Earthlink account, it would never even show up. I got "delayed" messages for a few days and finally a timeout/undeliverable. Repeatedly for weeks. Many other domain had trouble getting their emails to be accepted, but outgoing emails from the Exchange Server seemed to work OK.I played around with the threshold settings and other parameters in the IMF, and the filtering of spam responded to the changes, but no improvement in legit. email performance.Today, I decided to enable the POP3 service. It was off because nobody at this company uses it.Once I enabled it, all the emails began to arrive at the Exchange Server.What is the relationship between the POP3 service and SMTP on the Exchange Server? Why did this happen? I thought they were quite independent?

"Delayed" messages indicate the sending server was unable to communicate with the receiving server. Adjusting spam settings might affect whether or not a message is deleted/rejected, but it wouldn't ever cause "delay". As to your 2nd question, there is no way turning on or off pop3 would have any effect on your ability to receive inbound smtp mail. The issue must have been somewhere else. You can likely prove this by turning pop3 back off, to find mail is still flowing normally. You can also test from outside the network by using telnet to connect to port 25 and seeing what happens. If it doesn't answer, this could be the cause of the delays. If it does answer, and appears to be working fine, the problem is somewhere else.