How Does Email Get Delivered?

Your SMTP server then looks at who the message is to. Specifically it examines the domain it's supposed to get delivered to. This domain is then looked up via an online directory of sorts known as DNS (domain name service) to determine which server handles its incoming email. This special DNS host is known as the MX (mail exchange) record.

The receiving mail server is referred to the as the incoming SMTP server. Usually this is where the first level of anti-spam filter software is used. Most commonly one or more real-time blacklists are used to block messages from anyone who's not to be trusted.

In the simplest of cases, this SMTP server doubles as the POP3 server. POP3 is the protocol users use to download email messages from their server into their email client.

Frequently users will also have an e-mail spam blocker deployed client-side. Some emulate a POP3 server, and act as a proxy between your POP3 server and email client. Others act as a POP3 client, periodically poll the mail server for new messages to be analyzed.

Each approach has its advantages. The former is easier to configure. The latter may catch slightly more spam. Increasingly some email clients have simple spam email stopper technology included. This presents one more barrier an email has to pass through before making it to the user's inbox.

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