It’s possible to have a server act as a backup server, so in the unfortunate event that your main mail server goes down, mail gets queued up on the backup server until the main one is fixed.
Setting up PLESK to act as a backup MX server is fairly easy, here’s what to do.
Here’s some handy tips for managing your qmail queue on a linux machine, which can be helpful for debugging:
I managed to get a little email archiving system working which I am finding to be potentially quite useful in the future. The beauty of it is that every email going in and out the system is saved onto a google gmail account, which harnesses their power of filtering, searching and labelling!
This setup was specifically aimed at a PLESK-run box but I’m sure it would work on any box with a qmail/qmail-scanner enabled mailserver, actually any MTA with a Maildir format.
Qmail-Scanner is a very versatile tool for linux which allows you to scan any email that passes your system with various brands of virus scanners, including the open source ClamAV. Alongside the more thorough scan and possibility to audit content, I find the archiving feature very useful.
One particularly useful bit of qmail-scanner is that you don’t need to recompile qmail for patching, which can be a mamoth task on PLESK run systems (specifically VPSes in Virtuozzo)