POP and IMAP are pretty much dead at this point. Email is basically dead at this point. Want to spin up a machine and have it email you system messages? Nope. Want to run a Python script that sends to gmail? lol. https://mailtrap.io/blog/gmail-smtp/
On all my microservers I have pretty much have 22, 80, and 443 open. I try to interact exclusively over web ports for as much as possible.