Users often report getting spam messages that don't appear to be addressed to them. The To: line of the message will contain some other address, and the user wonders why the message was delivered to them at all.
The reason is that the To: line and the CC: lines in email are not actually used to route or deliver messages at all. Those are only informational lines that are part of the body of the message, and are called "message headers". And because they have no effect on message delivery, the content of those lines can be anything the sender wants them to be. Well-behaved email software always puts the actual recipients in the To: and CC: lines. But spammers don't follow the rules and don't use email software that follows the rules.
The actual recipient of a message is determined by what are called "envelope headers" which are set during the sending transaction between the sender and the email server. The sending software instructs the email server on who to send the message to during the sending transaction. The envelope headers also contain the IP number of the machine sending the message, and other information about the route the message took to reach you.
To see the actual address a message was sent to, you have to use the View All Headers feature in Web Mail. Most other email software also allows you to view these headers. Look for a header called X-ELNK-Loop. That is a special header inserted by the EarthLink mail server to always show the actual address the message was sent to by the sender. This will be the mailbox that the message gets delivered to, and since our server puts that header in there, it can't be faked.
So when a message shows up in your mailbox it is always addressed to you, but spammers will often hide this fact using bogus message headers.