2 SMTP

SMTP is “simple mail transport protocol”. However, the name is misleading, as the protocol itself is not simple, nor is its application.

The intent of SMTP is to deliver messages from an origin to a destination. A simplistic view of the use of SMTP is as follows:

• An email client program, such as Outlook or Thunderbird, “sends” a message to a recipient. Let’s assume the recipient is “tak@profs.org”. The message isn’t sent directly to the server with a domain name of profs.org. Instead, the message is sent to the SMTP server as configured in the email client program. This SMTP server is usually the SMTP server of the ISP of the sender. For our discussion, let say this is school.edu.
• The SMTP server of school.edu checks the incoming connection to see if it meets criteria of sorts. If everything checks out, the message is accepted and queue on school.edu for delivery.
• The SMTP server of school.edu sends all messages to be delivered on a first-come-first-serve basis. At some point, the message of this discussion gets sent to profs.org.
• The SMTP server of profs.org checks the message for a set of criteria. If everything checks out, then the message is delivered locally to a folder that belongs to tak the user. The message stays there until it is retrieved by either a POP3 or IMAP client.

This process seems simple enough, what can possibly be so complicated about it?