A couple of days ago, I wrote about considering a move from Postfix to Exim. I have just made that move on the main server. It took about three hours and was successful. Here’s what I learned.
My fears about Exim’s queue management being less sophisticated that Postfix were unfounded. It seems to do quite well.
Being able to reject viruses and spam during the SMTP conversation has turned out to be a huge win. I no longer have the dilemma of either dropping these messages on the floor or causing blowback by sending bounce messages to innocent victims of forged headers.
Exim has a nifty feature called synchronization detection. It happens that many ratware (spam-sending programs) have a poor implementation of SMTP, and Exim is able to detect this and filter out some spam before it hits any RBLs — simply because the sending spam mailer was behaving in a unique way. Very slick.
The configuration was not quite as easy as with Postfix, but clearly it has a lot more power. I think I’ve only scratched the surface so far. There’s a lot of cool stuff I can do yet.
Also, I shut off my backup MX. This thread over at debian-isp has an interesting discussion on the pros and cons of that. It seems that there are mostly pros.
One thing I didn’t go with was the SMTP transaction delays. They messed up some servers — well one in particular — and there is a valid point that they can increase load on sending mailing list servers.