Yeah, I’d recommend using rspamd for lower-end hardware over spamassassin. Might be a bit more work to set up, mostly because it’s not as popular, and there are fewer tutorials, but it doesn’t have the overhead from running on perl like spamassassin. That said, while there are people using rspamd on systems with 512MB of ram, they are usually smaller, personal setups that aren’t dealing with hundreds of emails a day.