Glossary
SMTP — Simple Mail Transfer Protocol
SMTP is the standard protocol for sending email between servers — typically port 25 for server-to-server relay and port 587 (or 465) for authenticated submission. SMTP alone does not authenticate senders — SPF, DKIM, and DMARC provide that layer.
Ports at a glance
25: MTA to MTA. 587: submission with STARTTLS. 465: implicit TLS (legacy). Blocking outbound 25 is common on consumer and some cloud networks.
FAQ
Is SMTP encrypted?
Often STARTTLS opportunistically — not required by the original protocol.
Who speaks SMTP?
Your mail client to your provider; your provider to the recipient’s MX.
Does SMTP validate identity?
No — that’s SPF/DKIM/DMARC on the message path.