Exchange Server stores all your data (messages, attachments, appointments, contacts, etc.) on the server until you explicitly remove it. Because of this, you must take precautions to ensure you do not run out of space on the server.
Faculty and staff mailbox quotas are set at 5 gigabytes (GB). You will receive a warning once you reach 4.5 GB and will have reduced mailbox functionality at 5 GB.
All mailboxes on Exchange Server 2010 are configured with mailbox limits. Faculty and staff have a mailbox quota of 5 GB. Messages in your Deleted Items, Drafts and Sent Items folders count towards your mailbox quota so be sure to clear these folders on a regular basis.
When your mailbox is over your limit, new incoming message will be immediately returned to senders with a notification that your mailbox is currently not accepting new messages. Once your mailbox size drops below your limit you will receive new messages.
Individual messages cannot exceed 25 megabytes (MB) in size. This includes the body of the message and all attachments.
If you are using OWA:
If you are using the full Outlook email client: