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Summary: This article discusses the “Mailbox size limit exceeded” warning in Office 365 and provides methods to set mailbox size limits for both single and multiple users using PowerShell. It emphasizes the importance of data backup and suggests using the Kernel Export Office 365 to PST Tool for a reliable backup solution.

Last week, a number of our Office 365 users received a “Mailbox size limit exceeded” warning. If you’ve encountered the same alert, there’s no need to be concerned. This warning simply serves to notify users that their Office 365 mailbox has reached the prescribed limit for sending and receiving messages.

It is crucial to address this warning promptly if you want your users to use their Office 365 account continuously. A wise practice is to take backup of all your older data and export Office 365 mailboxes to PST or any other secure format. Doing so will help you prioritize your emails and organize the mailbox effectively. Furthermore, to remove this warning from user’s accounts, you’ll need to set mailbox limits in your Office 365 account. To assist you in resolving this issue, we have outlined some methods to set Exchange mailbox size limits.

Methods to Set Exchange Mailbox Limit

The exclusive manual approach to establish Office 365 mailbox size limits for users involves utilizing the Exchange Management Shell. You have the flexibility to decide whether you wish to apply these limits to an individual user or multiple users.

Setting Mailbox Size Limit for a Single User
  1. Connect to Exchange Online using Remote PowerShell.
  2. After connecting to Exchange Online, run the below command to set the mailbox size limit for a single user.
    Set-Mailbox < UserID > -ProhibitSendQuota < Value > -ProhibitSendReceiveQuota < Value > -IssueWarningQuota <value>

    Note: In this command, the User ID represents the UPN, email address, or GUID or a single user. The Value parameter represents a number in MB, KB, or GB. See the below example to set the mailbox limit to 30 GB for single user.

    Set-Mailbox -ProhibitSendQuota 29GB -ProhibitSendReceiveQuota 30GB -IssueWarningQuota 28GB
  3. Now, check whether the current list of quotas is attached to the mailbox or not. You can use the below command to achieve this:
    Get-Mailbox < User ID > | Select *quota

Using this technique, you can easily set the Office 365 mailbox size limit for a single user.

Setting Mailbox Size Limit for Multiple Users

Setting mailbox size limit for multiple users is almost similar to a single user. However, there is a little difference in the PowerShell command that is used to set the mailbox size limit.

  1. Connect to Exchange Online using remote PowerShell.
  2. Once connected, run the below PowerShell command to set the mailbox size limit.
    Get-Mailbox | Set-Mailbox -ProhibitSendQuota < Value > -ProhibitSendReceiveQuota < Value > -IssueWarningQuota < Value >

    You can apply filters to either the Get-Mailbox cmdlet or the Get-User cmdlet to precisely target the users to whom you intend to apply these adjustments. Here’s an illustrative example involving three cmdlets used to filter the command for users within the sales department of an organization.

    Get-User | where {$_.Department -eq “Sales”} | Get-Mailbox | Set-Mailbox -ProhibitSendQuota < Value > -ProhibitSendReceiveQuota < Value > -IssueWarningQuota < Value >

Using the aforementioned command, you can effortlessly establish mailbox size limits for multiple users. Once these limits are in place, you will no longer receive the ‘mailbox size limit exceeded’ warning. However, if you continue encountering this warning, it indicates that your Office 365 subscription storage has reached full capacity. In such scenarios, simply deleting Office 365 mailbox data isn’t a viable solution due to the critical information it contains. Instead, the ideal course of action is to safeguard your data by taking an Office 365 backup using a reliable tool.

Kernel Export Office 365 to PST Tool

The manual methods to backup Office 365 mailboxes carry inherent risks of data corruption or loss. However, by utilizing this tool, you can set aside concerns about the security of your data. This tool stands out as one of the finest utilities to export Office 365 mailboxes to PST, offering the capability to back up even permanently deleted items in the PST format.

Using this software, you can quickly backup your Office 365 mailboxes and free-up storage in the Office 365 account to get rid of the “mailbox size limit” warning.


Addressing warnings such as “Mailbox Size Limit Exceeded” is imperative for Office 365 users. This article provides valuable insights into resolving this issue, offering effective techniques for its elimination. Additionally, we recommend a third-party tool that can prove invaluable for safeguarding your mailbox data before managing mailbox space constraints.