The link to part 3 from part 2 is broken (but the one in ToC works).

It doesn't mention reverse DNS (PTR for *.in-addr.arpa) records. Though not strictly necessary, but doesn't harm to have those set, and the author's mail server has those set.

Looks nice overall. The notable differences from how I set those are the lack of postscreen (including its greylisting), of a dedicated submission port, of SRV DNS records (_submission._tcp, _imap._tcp, _imaps._tcp), but presence/use of virtual hosts and users, and of OpenDMARC. Maybe I should try using the latter, though not sure how useful it is (whether it's worth the slight complication of the overall setup), when set on a small/low-traffic mail server.