Mail server

A mail server is a computer system or software service that handles part of email delivery. It can accept messages from another server, relay them onward, deliver them to a recipient's mailbox, or provide access to stored mail. A message may pass through more than one mail server before it reaches its recipient.

How does a mail server move a message?

When Alex sends a message to sam@example.com, the sending system looks up the destination domain's MX record to find a server that accepts mail for the domain, called a mail exchanger. It then uses SMTP, the protocol for transferring email between systems, to hand the message to that server. The receiving server may store the message in Sam's mailbox or pass it to another system.

The server listed in DNS is not necessarily the computer or service where a person reads email. A provider can use separate systems for message transfer, storage, spam filtering, and webmail. That is why a mail server and an email app are not the same thing.

Does a domain's website server handle its email?

Not necessarily. A domain can point its website to one provider and its email to another by using different DNS records. Changing a website's address records does not normally change the mail route; changing MX records can affect incoming mail without moving the website.

Related terms

• MX record — identifies a mail destination for a domain
• Email provider — offers mail services
• Email mailbox — the recipient destination
• DNS — publishes the routing information