What is SMTP, POP3, and IMAP?
Answer
These are email protocols. SMTP (Simple Mail Transfer Protocol) is used to send emails from a mail client to a mail server, and between mail servers. Port 25 (server-to-server), port 587 (client submission, with STARTTLS), port 465 (SMTPS — SMTP over SSL). POP3 (Post Office Protocol v3) is used to retrieve emails from a server to a local client (port 110, or 995 with SSL). POP3 downloads and typically deletes emails from the server — emails are only on one device. IMAP (Internet Message Access Protocol) also retrieves emails (port 143, or 993 with SSL) but keeps them on the server, synchronizing across multiple devices. Changes (read, delete, folder moves) sync everywhere. IMAP is the modern choice — use it when you access email from multiple devices (phone, laptop, browser).