To manage disk and resource usage, your administrator might enforce quotas to limit the amount of disk space your account can use.
To display your mail quota and how much you have used, hover the mouse over your name on the toolbar.
If you are over quota, the following things might happen:
Your administrator may have set up automatic purging of messages that are over a certain number of days old. Your administrator sets the policy for when messages are purged, how old they have to be, and which folders are purged.
If you hover your cursor over a folder, the number of messages in the folder and the size of the folder display.