Know how
Learn about the email terms and technologies that relay uses.
ARC
Sealed authentication results for forwarded mail
DKIM
Cryptographic signature for outgoing email
DMARC
Email authentication policy for SPF and DKIM
Feedback-ID
Grouping Gmail complaint data by stream in Postmaster Tools
MTA-STS
Enforce TLS for incoming mail connections
MX
Mail exchange records for domain email routing
PTR
Reverse DNS lookup for IP verification
Return-Path
Bounce address for email delivery notifications
SMTP
Protocol for sending email between mail servers
SPF
DNS record listing authorized sending servers
TLS-RPT
Reports about TLS connection failures