SUMail Limits

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.

Type	Limit	Notes

Type	Limit	Notes
Message rate limiting	30 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 limiting	10000 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 limit	3,600 messages per hour, per mailbox
User mailbox storage	100gb (active staff/faculty/student mailboxes)	warning: 98gb prohibit send: 99gb prohibit send/receive: 100gb
Shared/resource mailbox storage	50gb
Alumni mailbox storage	50gb
Archive mailbox storage	Unlimited	Available only for E3 licensed mailboxes
Messages per mailbox folder	1 million
Folders per mailbox	10,000
Message size limit	50mb	This includes attachments, but does not account for mime encoding or client limits.
Junk mail folder retention	30 days
Deleted Items retention	90 days
Inbox Forwarding Rule limit	10 Forwardee limit	The maximum number of recipients that can be configured for an inbox or transport rule with a redirecting action.