Hard. You need reverse DNS, which means you need to have a machine with a stable ip, and convince the network operator to set up a PTR reverse DNS record for you. This part is fairly easy if you are renting a VPS with a fixed ipv4 address, just ask the rental company.

You also need to set up mx, dkim, dmarc, spf, and a bunch of other stupid DNS records related to dane/tlsa/mta-sts that aim to put bandaids on top of bandaids on top of what is the shitty unsecured and unencrypted email protocol.

Then you need to fight with a bunch of arcane 90s Unix programs to actually not be gaping security holes that will allow people to relay off of your MTA and get you blacklisted worldwide. You need to fight with a milter and acme client to finally get the TLS stuff right too. Then there's the need to set up a spam filter for your inbox (probably).

> Then you need to fight with a bunch of arcane 90s Unix programs to actually not be gaping security holes that will allow people to relay off of your MTA

how many decades has it been since this was actually the default config?