GUIDE: Electronic Mail

E-mail is not a protocol. SMTP is a protocol. E-mail, and the protocols in use with e-mail sending/receiving, is complicated to integrate into a website natively. It will be easier to first learn by knowing the basics.

A general discussion will reveal there are many ports operating email. The below definitions help to explain some of the mechanics underlying the definitions.

  • Port 25 SMTP
  • Port 109 POP2
  • Port 110 POP3
  • Port 143 IMAP4
  • Port 465 SMTPS
  • Port 587 MSA (used by SMTP servers)
  • Port 993 IMAP4 (encrypted)
  • Port 995 POP3 (encrypted)
  • Other: 2525, 32587, etc.

SMTP client-to-server messages
Source: Postmark, Everything you need to know about SMTP (Simple Mail Transfer Protocol)
Internet Message Acces Protocol (IMAP)
Supports connecting multiple clients to the same mailbox simultaneously.
Mail Submission Agents (MSA)
Used by mail clients to submit messages for delivery by an SMTP server.
Post-Office Protocol (POP)
Stores messages delivered by SMTP. a.k.a. POP3 downloads the messages to recipient client.
Simple Mail Transfer Protocol (SMTP)
Used to transport mail for message relay. STARTTLS can be enabled.
Simple Mail Transfer Protocol Secure(SMTPS)
SMTP encrypted by implicit TLS.
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