Odd mail server behaviour

Question

Hi
For four days now I've been having a frustrating time with Mail on both my iMac and my old iBook. This has been happening on different wireless networks. I send an email from my main account, which is an IMAP account. I see the gear next to 'sending spin' for about ten seconds, then the progress bar goes to 99% in 'mail activity' ('outgoing mail'), then the email pops onto the screen witha delivery failure and I get given a choice of mail servers to choose to try again. Here's the thing - I select the very same server that the account in question is configured to use, and the email then goes instantaneously. This is happening with every single email I send on this account, the smtp details are configured correctly, but no email will go the first time.
I sync my mail rules etc. on mobileme, which is perhaps why this is happening on both of my machines, and the behaviour started on both at the same time, though they've both had the same mail smtp configuration for that account, unchanged, for over a year without any issues.
What's happening, and how do I get mail to work as it did?

Answer 1

You might also want to harden OSX.4 Tiger server against spam. I wrote an article which details implementing greylisting, blackholes, backscatter filtering, checking the sending mail server, recipient and email content. This supplements the anti-virus and spam checks already included in OSX Server to significantly reduce spam received and load on the mail server.
Go http://happymac.info/node/10