Overview
Exchange Online has various service limits designed to prevent spam, protect system performance, and ensure reliable email delivery for all users. Understanding these limits helps you manage your mailbox effectively and avoid email delivery issues.
Microsoft maintains detailed documentation about Exchange Online limits at Exchange Online limits. This page is updated regularly as service features evolve.
Detail
Key Limits to Know:
Mailbox Storage
- Primary accounts (A5 license): 100 GB storage quota
- Alumni accounts (A1 license): 50 GB storage quota
- Warning threshold: Alerts begin at 98-98.5% of quota (98 GB for A5, 49 GB for A1)
- Prohibit Send: Mailbox stops sending at 99 GB (A5) or 49.5 GB (A1)
- Prohibit Send/Receive: Mailbox stops all email at 100 GB (A5) or 50 GB (A1)
Message Size and Sending
- Maximum message size: 150 MB (Outlook), 112 MB (Outlook Web App)
- Daily recipient limit: 10,000 recipients per 24-hour period
- Message rate limit: 30 messages per minute
- Recipients per message: Up to 1,000 recipients (customizable by admins)
Receiving Limits
- Hourly receiving limit: 3,600 messages per hour from all sources
- Single-sender limit: 33% of the overall receiving limit (approximately 1,188 messages/hour from one sender)
What to Do If You Approach a Limit:
- Storage issues: Delete unnecessary emails, empty your Deleted Items folder, or archive old messages
- Sending limits: If you need to send bulk legitimate email (newsletters, announcements), contact Pitt Digital to discuss appropriate solutions
- Receiving limits: If a mailbox exceeds receiving limits, wait one hour for the limit to refresh
Last verified: January 2025
Related Information
For the most current information about all Exchange Online limits, including attachment limits, folder hierarchy limits, and retention policies, please refer to Microsoft's official documentation.