@atomicpoet i have a pi 400 running postfix. my ISP blocks port 25. idk about port 465: i port scanned the big email providers and IIRC 465 seemed to be inactive. Wikipedia suggests port 465 is obsolete and everything uses port 25 with SMTP commands that install the security layer without changing the port.

if your ISP blocks port 25, an easy solution is to get a VPN which doesn't block port 25 and connect your host to that. that's my setup atm which i use for receiving email. i haven't tried sending email yet: i'm working with OVPN to provision a PTR record for my VPN's address before i try it, because i don't want to end up on a blacklist.

per my experience so far, self-hosting email is about an order of magnitude more involved than self-hosting something like Pleroma, just for comparison.