There are various service limits for SUMail that are designed to protect the email service as a whole and detect anomalies such as compromised accounts. The following list breaks out limits that would most likely affect all email users, and for a complete list of service limits check the following link: 
Exchange Online limits - Service Descriptions | Microsoft Docs

All active Students, Staff, and Faculty are on an E3 license plan. Alumni are E1, and inactive users aren't licensed. Shared/Resource mailboxes also do not receive a license since they are not directly logged into.



Message rate limiting30 email submissions per minute, per mailbox

There are no overrides for this.

No sent messages are lost or denied, they will sit in users outbox until the next minute and send as many as possible.

Recipient rate limiting10000 recipients every 24 hours, per mailbox

Specifies the total number of email addresses which can be mailed to in a 24 hour period, whether unique or not.

Receive rate limit3,600 messages per hour, per mailbox
User mailbox storage100gb (active staff/faculty/student mailboxes)
  • warning: 98gb
  • prohibit send: 99gb
  • prohibit send/receive: 100gb
Shared/resource mailbox storage50gb
Alumni mailbox storage50gb
Archive mailbox storageUnlimitedAvailable only for E3 licensed mailboxes
Messages per mailbox folder1 million
Folders per mailbox10,000
Message size limit50mbThis includes attachments, but does not account for mime encoding or client limits.
Junk mail folder retention30 days
Deleted Items retention90 days
Inbox Forwarding Rule limit10 Forwardee limitThe maximum number of recipients that can be configured for an inbox or transport rule with a redirecting action.