April 1st, 2013

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).
READ FULL ARTICLE:
http://abneyassociates.org/protocols_/smtp/