SMTP Explained: Ports, Spoofing and SPF, DKIM, DMARC for Network+
SMTP — Simple Mail Transfer Protocol — is how email gets sent . That word matters, because the most common exam trap on this topic is confusing sending with retrieving. SMTP pushes mail out. POP3 and IMAP pull mail down. One protocol for sending, two for receiving. When you click Send, your client hands the message to a mail server over SMTP. That server finds the recipient's mail server and relays it there, again over SMTP. The message then sits in the recipient's mailbox until their client collects it — and that collection uses POP3 or IMAP, never SMTP. The Ports Port Use Encryption 25 Server-to-server relay Opportunistic STARTTLS, historically none 587 Client submission — the modern standard STARTTLS, authentication required 465 Client submission, implicit TLS SMTPS — encrypted from the first byte 2525 Unofficial alternative Varies — used when 25 is blocked The distinction between 25 and 587 is worth understanding rather than memorizing. Port 25 is for serv...