In the process of setting up a mail server for a collegue the other night (in order to deliver mail from 6+ domains to one IMAP account) I found an interesting quirk.
After you've set up and configured a working e-mail server, with all the UBL checks and correct delivery methods in place -- if you find other SMTP transactions work OK, but the local client can't connect and you're with Optus (In Australia), go here to turn off the automated port 25 block.
Thinking on though, this procedure unblocks port 25 globally, leaving one open to the prospects of exploit code spamming people by using port 25 on the local machine -- after all, the mail server wasn't on the persons local machine or even their LAN, but halfway across the world -- the Optus site makes reference to the unblocking process being for advanced users -- wouldn't advanced users be better off leaving the block in place for all sites not in a list?
(Yes, the server could use SSL, or even be on a different port -- both would be viable alternatives to opening SMTP from a customer premises to the world)
