I’ve been using Qmail since 2000, and as an ISP, it’s saved my rear end more times than I can tell you compared to other Email servers I’ve had to deal with… I’ve been lurking on the QMT lists via the web for years, and finally decided to join the list.
Largest we got for a while was over 500 domains with various email sizes. What I found I had to scale was the /home directory, namely under the /home/vpopmail/domains area by, if needed, creating separate partitions for each area [example 0,1,2,etc…]. I do remember that if you take the default of just creating a partition, you could easily run out of inodes. I’ve had to create the partitions like this: mke2fs -g 16384 -b 2048 -i 2048 -T small -j -L /home /dev/cciss/c0d0p6 Reason I had to do this was I would have plenty of free space, Terabytes even, and could not write to the drive. Obviously, change it to meet your needs but if you want to continue to use ext4, watch the inode sizes. I’ve run the ISP email server on HP Proliant with only twin Dual core processors and 4Gb of memory. My new one, and part of the reason I’m on the list now, is under CentOS 7. The only difference in size is more memory [caching for the hard drives]. I think you find, Alex, that the RAM and Disk speeds matter more than CPU with Qmail, it’s that efficient. I started on an old P4 400Mhz with 1Gb memory and a couple of domains. So scaling Qmail out is not all bad. The only time I’ve seen CPU intensive on the system is on a reboot, you may find fail2ban to take a CPU for itself while it catches back up on the log file. This is why I would recommend at least 4 vCPU. So, to answer your question, Alex, I would say you’re more likely to increase RAM and Disk space as you grow. As to backup, Eric hits a great point. If possible, I recommend that you run the system as a VM so you can snapshot it and get a very consistent backup of the email databases. And to everyone’s hard work on the list, thank you so much! Carl C.
