What's the difference between a mailbox and an e-mail address? A mailbox can be compared to a letterbox:
A few examples:
Should you get an extra e-mail address or an extra mailbox?
If you have small children and want to control their e-mails, it's better to add an extra e-mail address to your existing mailbox. If you want your children to have their own mailbox, add an extra mailbox to your account.