Email uses SMTP to push messages between MTAs (and from MUA to submission server), while IMAP/POP3 let clients pull from a mailbox. Modern deployments use STARTTLS or implicit TLS (ports 465/993/995) — plaintext SMTP on port 25 is for server-to-server only.
Sending an email
✍️
MUA compose
User agent
📤
SMTP submit
Auth to provider
🔄
MTA relay
DNS MX lookup
📥
IMAP fetch
Client reads mailbox
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