Usage Limits for Microsoft 365 (M365) Email

Why Do We Need Limits?

We enforce mailbox and message size limits in Microsoft 365 to maintain optimal performance across our mail servers and ensure reliable email service for all users.

Mailbox Quota and Notifications

Each user in Microsoft 365 is allocated a 50GB mailbox quota. The system uses automatic notifications and restrictions to manage space usage:

• Warning Notification: You will receive a warning when your mailbox reaches 49GB.

• Sending Restriction: You will no longer be able to send emails once your mailbox reaches 49.5GB.

• Receiving Restriction: Incoming messages will be rejected when your mailbox reaches 50GB.

These thresholds help users take action before hitting hard limits that block email activity.

Email File Size Limits

Microsoft 365 enforces a 50MB maximum size limit on individual email messages. This includes all content and attachments.

• Messages larger than 50MB cannot be sent or received.

• For larger files, users are encouraged to use OneDrive or SharePoint links to share documents.

Check Your Mailbox Size

To monitor your mailbox usage in Outlook:

1. Click File in the Outlook desktop client.

2. Select Tools > Mailbox Cleanup.

3. Choose View Mailbox Size.

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