> What are the memory requirements for postfix, dovecot, and rspamd these days?

Approximately nothing. I run all my email infrastructure on the smallest available $5/mo Linode and it's way overprovisioned even so. I'd take a smaller VM if they offered one.

Hmm. Admittedly, I didn't use postfix, but dovecot was the largest process running on my 1G server and adding rspamd resulted in it doing the Out-of-memory mambo a couple of times a week. This was just for my domain, but I do get a crap ton of spam.

Very low for one person with a few emails per day. They almost never appear in top on a 3€/month VPS server (2 vCPU, 2G RAM).

They probably work well on quite limited hardware. But I guess it largely depends on traffic / on the number of hosted users.

Doesn’t even need that. I’ve run pretty much that stack on an original Raspberry Pi. You wouldn’t want to be trying to do a lot else, and GB sized attachments are gonna be limited by the usb Ethernet speed, but it’ll run just fine.