Mail server systems use the DNS -- Domain Name System. When one is about to deliver a piece of e-mail, it looks at the address and queries the DNS (there are system calls to do this) to determine to what system(s) to send the e-mail. If the e-mail should go to a mail exchanger (MX), as most Internet e-mail does today, the MX record for the address will point to the systems that claim to accept mail for the particular domain.
For more information on this topic, visit these other searchSecurity resources:
Best Web Links: E-commerce Privacy Issues
Chat Transcript: Email security
Dig Deeper on Email and Messaging Threats-Information Security Threats
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.