What is the email quota on Exchange?
The default quota (how much storage space is allowed for each person including the space required to store all e-mail, calendar data, contact information and task management data) for each mailbox is 250 megabytes (250MB). When a user exceeds their quota a warning message is issued. When a user exceeds their quota by 50MB the user is prohibited from sending e-mail. When a user exceeds their quota by twice the original quota the user is prohibited from sending and receiving e-mail.