SMTP

Simple Mail Transfer Protocol is the web standard for email transmission using port 25 or 587 (MSA). It conducts secured connections via SSL (SMTPS).

This is a text-based protocol wherein a mail sender communicates with its receiver through giving its instructions over TCP connection. However, it only defines the message transfer and not its content (i.e. like the physical mail envelope and not the body of the letter).

User-level client programs for email can only use this protocol for outoing messages; for clients to retrieve emails, IMAP/POP is used instead. But for mail servers, they can use SMTP for both sending and receiving emails.

This themes includes code from Andreas Hassellöf, licensed under a Creative Commons Attribution v3.0 License