Every email is sent to an address, e.g. xyz@gmail.com. This is the most important piece of information to deliver an email to its destination.

First, the email is delivered to the machine "gmail.com". On this machine, there are mailboxes for every name including "xyz". The email is stored in the mailbox named "xyz".

Later when the user "xyz" logs in and accesses the mailbox, the email is shown to the user.

When an email is sent to multiple recipients (e.g. xyz@gmail.com and xyz@yahoo.com), copies of the email are delivered to each of the recipient.