This is an old revision of the document!
In order to have a working SMTP server we have to take care of “some” ;) points:
PTR reverse DNS
dig +short ptr <reverse IP>.in-addr.arpa
must give an hostname which DNS
A record points to the <IP address> of your server.
MX → who exchange the mail for the domain?
SPF → which addresses can be originated from the MX?
DKIM → how are signed messages outgoing from the MX?
DMARC → what actions do you suggest to mail receivers' providers regarding the conf of SPF/DKIM and where you would like to receive reports from them to tune your mail settings?