Everything required for mail to work.
MX RECORDS
Where mail for your domain should be delivered. Without them, incoming mail fails.
THE MAIL HOSTNAME A RECORD
MX records point at a hostname, which must itself resolve. mail.yourdomain.com needs an A record.
SPF
A TXT record listing which servers may send for your domain.
One record only.
DKIM
A TXT record holding a public key, used to verify signatures on your outgoing mail.
DMARC
A TXT record at _dmarc.yourdomain.com stating a policy for mail failing the other checks.
Optional and increasingly expected.
WHERE TO FIND WHAT YOURS SHOULD BE
cPanel > Email Deliverability shows the expected records for each domain and indicates problems.
That screen is the reference. Compare what is published against what it says.
IF YOUR DNS IS EXTERNAL
All of these must be created at the external provider. cPanel's zone is ignored.
THE ORDER OF IMPORTANCE
MX for receiving. SPF and DKIM for sending. DMARC for policy.
