MailX
Check your domain's SPF, DKIM, DMARC and mail servers, and get the exact record to add.
What these records do
SPF
Lists the servers allowed to send email for your domain.
DKIM
Signs every email so receivers can tell it really came from you.
DMARC
Tells receivers what to do with email that fails SPF or DKIM, and protects your name from spoofing.
Reverse DNS
A mail server without one is often treated as spam.