One additional (non-security) feature that this guide missed is a reverse PTR record for your server's IP address. You'll have to set this on the side where you get your IP address from rather than in your own DNS, but lacking it will get your email classified as spam even if you implement all the other protocols. Basically, when your mail server says "EHLO mail.chamaris.tld", the other side will try to validate that the IP address you're connecting from actually points to mail.chamaris.tld.

Furthermore, you need to pick a host that takes action when their IP addresses appear on blacklists. Microsoft, particularly, uses UCEPROTECT as a blacklist source, and that particular company will blacklist and entire ASN if they receive too much spam from a particular IP address block (that doesn't get resolved in time).