fulltime email server - storage configuration

[coreywi]

I'm thinking about a replacement email server on a PI. This includes servicing multiple email domains, 1000's of emails, and a mySQL database. Packages include postfix, dovecot, spamassassin, mySQL, etc., etc.

I've got a PI3B+ and PI4 to choose from along with an external USB3.0 SSD. I'd like to decommission a full desktop computer that is 6+ years old and is probably on it's last legs. Thought a PI-based server might be a easier-to-maintain alternative.

I'm buying high quality power supplies and a redundant PI, etc. Ultimately, I'd like to reduce the risk of storage failure as much as possible. I understand that SD cards do not like lots and lots of writes and that it can be hit-and-miss sometimes that the card you use will last.

I'd like to put everything on an external USB 3.0 HDD/SSD, but I understand the PI4 won't have that capability for awhile. The PI3B+ has boot-from-USB capability (USB 2.0) but the performance is nothing against the PI4 - both for CPU and i/o throughput.

So I thought about a PI4 with read-only OS partitions on the SD card and having the data directories symlinked to the external SSD for all the dynamic stuff stuff.

Any comments/suggestions would be appreciated.

[rpdom]

Simpler to have just the /boot partition on the SD card (which hardly ever gets written to) and the rest of the system on the SSD.