SMTP
Simple Mail Transfer Protocol — the standard for sending email between servers.
Published January 15, 2026 · By RAPID SMTP
SMTP is the protocol email clients and servers use to push messages toward a recipient's mailbox. It has been the internet standard since RFC 821 in 1982. Modern SMTP runs over port 587 with STARTTLS or 465 with implicit TLS.
Related terms
- DKIM (DomainKeys Identified Mail)A cryptographic signature added to every outbound email that proves it came from your domain.
- SPF (Sender Policy Framework)A DNS record that lists which servers are allowed to send mail for your domain.
- DMARCA DNS policy that tells receivers what to do when SPF or DKIM fail.
- SMTP relayA service that accepts your outbound mail and forwards it to recipient servers on your behalf.