What is Mailbox Quota in Microsoft 365?

Mailbox Quota in Microsoft 365 refers to the maximum storage limit assigned to a user's mailbox in Exchange Online. When a mailbox reaches its quota, users may be restricted from sending or receiving emails until storage is freed up.

Key Components of Mailbox Quota

1. Mailbox Storage Limit
   • Different Microsoft 365 plans have varying mailbox quotas.
   • Example:
   • Microsoft 365 Business Standard: 50 GB mailbox
   • Microsoft 365 E3/E5: 100 GB mailbox
2. Warning & Restrictions
• Warning Threshold: Users receive an alert when the mailbox nears its quota.
• Send Restriction: Users cannot send emails once the quota is exceeded.
• Send & Receive Restriction: Users are completely blocked from sending and receiving emails once the hard limit is reached.
3. Archive & Auto-Expansion
• Some plans include Online Archiving to extend mailbox storage.
• Auto-Expanding Archive allows additional storage beyond the primary quota

How to Check Mailbox Quota

Users can check their mailbox quota in Outlook or using PowerShell:

Get-MailboxStatistics -Identity user@domain.com | Select TotalItemSize

Admins can check organization-wide quotas:

Get-Mailbox | Select DisplayName, ProhibitSendQuota, ProhibitSendReceiveQuota

Best Practices for Managing Mailbox Quotas

1. Enable Archive Mailboxes Move older emails to an archive to free up space.
2. Set Retention Policies: Automatically delete or archive old emails to optimize storage.
3. Monitor Usage: Regularly track mailbox usage to prevent disruptions

Mailbox Quotas help maintain email efficiency and storage management, ensuring users can continue working without disruptions.

Explore More

Checking Mailbox Quota Using PowerShell