Mailbox size is determined by the size of the folders inside it.
As you can see in the illustration on the left, your mailbox is made up of subfolders. The size of the mailbox is determined by the size of each subfolder inside it. As you send and receive messages, make appointments, create tasks or notes, and record journal entries, these folders fill up, so your mailbox starts to fill up too. We'll tell you how to see mailbox size next. You'll also get a chance to see the size of your own mailbox in the practice session at the end of this lesson.
Who sets the limits? If you store your e-mail on a server, your mailbox size limitations are usually set by a system administrator. Size limitations can vary greatly and can be anywhere from 1 megabyte (MB) to 90 MB or more.
Not sure where your e-mail is stored? If you get periodic nasty notes from the system administrator, chances are that your e-mail is stored on the server.
What happens when a limit is reached? Once a mailbox reaches its upper limit, an administrator may start limiting functionality: for example, at 90 MB you may get a warning; at 100 MB you may no longer be able to send e-mail; and, at 110 MB you may no longer receive e-mail.