Email Protocols Overview

Overview

This lecture explains the protocols used to send and receive email messages, focusing on IMAP, POP3, SMTP, and their roles in the email lifecycle.

IMAP (Internet Message Access Protocol) stores emails on a remote server, enabling access from multiple devices and users.
IMAP uses port 143 for non-encrypted and port 993 for encrypted (SSL) communication.
POP3 (Post Office Protocol 3) downloads emails to a local device, offering offline access and freeing up server space.
POP3 assumes single-user access and usually deletes emails from the server after download, complicating multi-device sync.
POP3 uses port 110 for non-encrypted and port 995 for encrypted connections.

SMTP (Simple Mail Transfer Protocol) is the primary protocol for sending email from a client or server to another mail server.
SMTP requires no authentication by default, making spam possible, but modern servers restrict relaying.
SMTP uses port 25 (non-encrypted), and ports 465 or 587 (encrypted via SSL).
SMTP relay servers help prevent emails from being flagged as spam, especially for bulk or transactional emails.
Using third-party SMTP relay services can improve deliverability and avoid overwhelming your own server.

HTTP/HTTPS is used to access web-based email services like Gmail but is not a mail protocol itself.

Email is composed and sent via SMTP from the sender’s server (MTA) to the recipient’s server.
The recipient’s server delivers the message to a Mail Delivery Agent (MDA).
The recipient accesses the email using POP3 or IMAP.

IMAP — Protocol that keeps emails on a server for access from multiple devices.
POP3 — Protocol that downloads emails to a client, often deleting them from the server.
SMTP — Protocol for sending emails between servers or from client to server.
MTA (Mail Transfer Agent) — Software that transfers email between servers.
MDA (Mail Delivery Agent) — Software that delivers emails into the recipient’s mailbox.
SMTP Relay — Service/server that forwards outgoing mail, aiding in deliverability and spam reduction.
HTTP/HTTPS — Protocols for web communication, used to access webmail interfaces.

Review differences between IMAP, POP3, and SMTP and memorize port numbers.
Decide on IMAP or POP3 based on your device access needs.
Consider using SMTP relay services for bulk or transactional email.
Optional: Research proprietary protocols (e.g., MAPI) or set up your own email server.