This article is written for Microsoft Exchange administrators and provides information on the storage and recipient limits available in Microsoft Exchange Online. 

Note: The storage and recipient limits information provided in this article does not reflect the limits that UChicago provides. UChicago Microsoft Exchange administrators can contact IT Services for support if needed.

Microsoft Exchange storage and recipient limits fall into one of the following categories:

• Address book limits
• Mailbox Storage Limits
• Capacity alerts
• Mailbox folder limits
• Message limits
• Receiving and sending limits
• Reporting and message trace limits
• Retention limits
• Distribution group limits
• Journal, Transport, and Inbox rule limits
• Moderation limits
• Exchange ActiveSync limits

You should also be aware that:

• When a limit is changed in the Microsoft data centers, it can take some time to apply the change to all existing customers.
• You can't modify most of these limits, but you should be aware of them.
• These limits apply to both internal and external recipients.
• By default, Exchange Online Protection (EOP) protects Exchange Online mailboxes.
• For limits that apply to EOP features in Exchange Online, see Exchange Online Protection Limits.