As I check user mailbox limits regularly when I find a user that is nearing their limit they get an email message from me similar to the following:

“You are not far away from reaching your mailbox storage limit so now would be a good time to reduce the number of items in your mailbox. Check your inbox, sent items and deleted items folders as emails tend to lurk there, also check for unnecessarily large emails or emails with large attachments (you can always save the attachment). Remember, as you near your storage limit you will begin to receive automated warnings, if you exceed your storage limit your mailbox will be automatically shutdown.

Storage Limits are in use to keep the email system from getting clogged up and to ensure timely backups of valuable information.

Check your mailbox size by right-clicking on Outlook Today, then clicking Properties and finally clicking Folder Size. To see the size of each message then right click in the field headings of the inbox or sent items then select Field Chooser. Find the item in the Field Chooser Box that says ‘Size’ and drag it into your heading bar. This will now show the size of individual email messages.”