UMD Google Mail maintains sending limits on email messages in order to ensure the health, safety and security of all accounts. If you exceed the sending limits, you may see one of the following error messages:
The limits restrict the number of messages sent per day and the number of recipients per message. After reaching one of these limits, a user cannot send new messages for up to 24 hours, but they can still access their account and receive incoming email. Limits per day are applied over a rolling 24-hour period, not based on a specific time of day.
For more information on students' email account, see Email for Students (TERPmail).
To learn more about Google Mail sending limits, view the Google Apps email sending limits article.
Content courtesy of Google Apps Help