SMTP

Simple Mail Transfer Protocol
SMTP is an internet standard for e-mail transmission across IP networks.

Most e-mail systems that use the internet to send mail use SMTP, they uses it send messages from one server to another, where the messages then can be retrieved by an e-mail client using POP3 or another client IMAP..

SMTP works by:
 * 1) Your e-mail client Connects to the SMTP server through port 25
 * 2) The client tells the SMTP server all the information about the message, the sender, recipient, as well as the message
 * 3) The SMTP server then take the recipients address (abc@def.com) and breaks it down into the name (abc) and the domain name (def.com). If you are sending an e-mail to a differrent e-mail client than the one you are using SMTP needs to communicate with the domain, if not SMTP server passes the message over to the POP3 server.
 * 4) SMTP server asks the DNS (Domain Name Server) for the IP address for the e-mail client you are sending to (def.com)
 * 5) The SMTP server then connects with the SMTP server def.com uses through port 25, telling it the senders adress etc. Then it gives the message over to def.com's SMTP server how passes it onto its POP3 server, which puts the e-mail to the recipients mailbox