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Microsoft 365 - Unable to send/receive messages due to mailbox quota

When an Office 365 account/mailbox (NetID or service account) reaches its mailbox quota, it will no longer be able to send or receive messages. The mailbox quota calculation includes all email and calendar data (including any attachments) within the account/mailbox. Note: OneDrive space is excluded from mailbox quota calculation/limit.

Can mailbox quota be increased?

Mailbox quota cannot be increased.

There are three kinds of notifications when a mailbox is nearing, or at, capacity:

The user receives an email warning that the mailbox is approaching the maximum size limit. This warning is intended to encourage users to delete unwanted mail. Received when mailbox reaches 49/99 GB depending on account type.
Prohibit Send
The user receives a prohibit-send notification email when the mailbox size limit is reached. The user cannot send new messages until enough email is deleted to bring the mailbox below the size limit. Received when mailbox reaches 49.5/99.5 GB depending on account type.
Prohibit Send/Receive
Prohibit Send/Receive Exchange Online rejects any incoming mail when the mailbox size limit is reached, and sends a non-delivery report (NDR) to the sender. The sender has the option to try resending the mail later. To receive messages again, the user must delete email until the mailbox is below the size limit. Received when mailbox reaches 50/100 GB depending on account type.

What can I do to keep my mailbox below my quota?

Important: There are no system backups for Office 365 accounts. Once a message is deleted and expunged from your recover deleted items location, it cannot be restored.

  • Use Outlook on the web to delete unwanted messages/folders - make sure to empty the 'Deleted Items' folder after delete the messages/folders.
  • Clean up mailbox data.
    1. Go to Outlook on the web.
    2. Within Mail sub-section, click Clean up mailbox.
  • Backup your data
  • Move mailbox data to another account - contact your local IT support staff to discuss these options.
  • If you are unable to delete anything further you may have a full "Recover Items Deleted From This Folder". This folder can hold 30GB of data and the items will only be permanently deleted after 30 days.
    • To delete the items go to the Deleted folder > at the top there will be a link called "Recover Items Deleted from this Folder" > select All > Purge from this folder > It will then ask "Do you want to permanently delete the selected items" > Select "yes" then the items will be deleted. 

Note to IT support staff - one possible temporary solution is to create a service account to move data to which the customer does not access daily but cannot be deleted due to data retention policies/needs.

Other resources

Keywordsmicrosoft ms office365 o365 m365 microsoft 365 full send receive emails messages over quota mailbox empty unable cleanup limit deleted items recover backup manage no more space Warning Prohibit Send/Receive license changeDoc ID91248
OwnerO365 S.GroupMicrosoft 365
Created2019-04-23 08:31:45Updated2023-10-05 15:36:32
SitesDoIT Help Desk, Microsoft 365
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