No you’re right, I shouldn’t discourage, just wanted to warn it’s not the same as most other self hosting projects, where often you just need to spin up a docker container.

Yeah, this is very fair! I just wanted to also provide the other perspective. Self hosting e-mail is very doable, and I think there are some things like mailcow / mail-in-a-box that make setting up the software on the server a lot easier (I haven't used these, but I've heard good things)... But you're probably still going to have to double check your rDNS and make sure to add the appropriate DNS entries... And you might not even realize that you have to do that, and then you're like "why the hell can't I send e-mail to anybody", and it's not the easiest thing to debug (especially if you haven't set up DMARC entries for getting reports from other mail servers). Plus... If you get the DNS entries wrong it can be a pain to wait for the TTL to expire to make changes. The setup definitely isn't without its headaches and hassles, but it's not impossible and once it's good to go you probably won't have to change anything.

FWIW hasn’t DNSSEC/DANE been added to the prerequisites these days or is that still optional?

This is currently optional afaik. I believe you can use this to establish that your e-mail server accepts TLS so other mail servers can know not to downgrade to an unencrypted connection. Admittedly, I'm not super up to date on this, and I'm slightly confused about the differences between MTA-STS and DANE. Also fwiw, I think both of these solutions mainly impact receiving mail, and shouldn't make much of a difference if any for you sending mail to the big providers.

Okay, so I did some research to confirm my previous understanding and for the sake of completeness I just wanted to throw this information into this thread... Neither DNSSEC/DANE nor MTA-STS is required. AFAIK none of the huge e-mail providers like Gmail, Outlook, or iCloud implement DNSSEC/DANE, but protonmail and tutanota both do. Of those everybody implements MTA-STS, except for iCloud.

In the case of e-mail both of these aim to alleviate a big security flaw in e-mail, which is that when Alice is trying to send you an e-mail, Alice's mail server has no clue whether or not your e-mail server supports TLS (e-mail is older than TLS, so it's bolted on in an opportunistic fashion)... As a result if somebody can get in the middle of Alice's mail server and your mail server they can say "hey, I don't support TLS", and then Alice's mail server will just say "okay, fine, here's the e-mail unencrypted". Obviously such a downgrade attack is BAD, so DNSSEC/DANE and MTA-STS are attempts to prevent this from happening.

DNSSEC/DANE solves this problem because it guarantees that DNS records are legitimate and it can guarantee whether or not a DNS record that says "hey the mailserver supports TLS" does or doesn't exist. The disadvantage of this is just that it relies on DNSSEC, which has its own caveats.

MTA-STS attempts to mitigate the problem... With MTA-STS you add some DNS records that say "hey, look up the MTA-STS policy from this HTTPS server", and the HTTPS server provides a file that says whether or not the mail server requires TLS connections to prevent downgrades. This always bothered me, though, because if somebody can attack DNS this arguably gives you very little... And if somebody is in the position to block HTTPS traffic they can prevent the policy from being fetched as well. Theoretically this doesn't provide much of a guarantee, but I guess in practice it's probably a decent mitigation because if a policy has been fetched before there will be a cached version available, so you'd need a sustained or well-timed attack to break MTA-STS, and on the plus side they can't generate a bogus policy file to disable TLS connections to the mail server unless they can get a valid TLS certificate for your domain.

Either way, both of these things are pretty much entirely about receiving e-mail, and aren't spam mitigation measures, so they shouldn't have anything to do with your ability to send e-mail (which is the harder part). It matters for sending in the sense that you don't want e-mail that you send to other mail servers to get downgraded from TLS when it shouldn't either, which means your mail server should validate MTA-STS + DNSSEC/DANE for mail servers that you are sending mail to. Ideally you would set up DNSSEC/DANE and MTA-STS in order to prevent this class of attacks on your personal e-mail, though it's not strictly necessary. MTA-STS is pretty trivial to set up as long as you already have an HTTP server on hand to serve up the policy file (which you probably do). DNSSEC may be a heavier ask for people depending on TLD support, registrar support, nameserver support, and software support (a lot of the DNSSEC signing software coughldnscough seems to choke on certain RRs -_-), but this may be easy for many people to implement.