I agree, mail deliverability is really hard.
In my case, the mailserver is only used to use a custom email address and forward the email, so deliverability was not an issue but other people using my domain name to send phishing emails. By making the fixes mentioned in the article the phishing attacks were stopped.
>Hostgator -> cPanel -> Email Authentication
...is ignoring 99% of the complexity and long term maintainance that DKIM implies.
And why bother? It's not like the mega-corp walled gardens care if you have the perfect mailserver implementation. They'll mark you as spam or blacklist you anyway, because they can, because it's easier, because it's a job someone's doing for profit and you don't effect that.
No. An SPF record is enough for determining if mail is legitimately from it's real mailserver. DKIM is cargo cult nonsense for most cases. A sacrifice to the google/microsoft/apple gods to hopefully earn their favor, but one that is almost always ignored anway.