Read time: 7 minutes
If you are getting the Exchange Online mailbox size warning notification, it means your mailbox size has crossed the predefined size limits. Do not worry, it is not an error but a notification to alert you so you can manage the allocated size limits. But fixing it is crucial because if you leave it as it is, soon you will not be able to send or receive any email.
There are two simple methods to resolve the Office 365 mailbox size warning. First is to increase the predefined limits, like if it was 50 GB earlier, then set it up to 100 GB. The second method is to either delete obsolete data or archive the mailboxes locally on your system. In the following sections, we will discuss both these methods in detail. But before that, let’s take a look at the mailbox size limits based on different Office 365 plans.
Office 365 Mailbox Size Limits by Plan
Microsoft offers several business and enterprise plans for different use cases. The mailbox limits set by Microsoft for all different plans are:
| Primary Mailbox | Archive Mailbox | Shared Mailbox | Resource Mailboxes | Public Folder Mailboxes | Group Mailboxes | |
| Microsoft 365 Business Basic and Standard | 100 GB | 50 GB | 50 GB | 50 GB | 100 GB | 50 GB |
| Microsoft 365 Business Premium | 100 GB | 1.5 TB | 50 GB | 50 GB | 100 GB | 50 GB |
| Microsoft 365 Enterprise E3/E5 | 100 GB | 1.5 TB | 50/100 GB | 50 GB | 100 GB | 50 GB |
| Office 365 Enterprise E1 | 50 GB | 50 GB | 50 GB | 50 GB | 100 GB | 50 GB |
| Office 365 Enterprise E3/E5 | 100 GB | 1.5 TB | 50/100 GB | 50 GB | 100 GB | 50 GB |
| Office 365 Enterprise F3 | 2 GB | NA | 50 GB | 50 GB | 100 GB | 50 GB |
Note: The above limits are for business and enterprise plans. Standalone plans have different storage limits.
In most organizations, when the mailbox size is almost 98% full, an Exchange Online mailbox size warning notification pops up. To fix this, you need to manage Exchange mailbox size and make sure it is within the defined limit.
Methods to Resolve Office 365 Mailbox Size Warning
The fastest way to resolve it is by increasing the mailbox size limit. If that is not possible, you must free up space in the mailbox. Both of these methods are given below:
Method 1: Increase the Mailbox Size Limit
In most Office 365 plans, the user usually gets a 100 GB primary mailbox size. But often administrators set up the Exchange Online mailbox size warning notification to pop up at 70 or 80 GB instead of the usual 98 GB limit.
Ask your admin if that is the case with you, and if it is, then ask them to fix it. If you are the admin, use the Exchange Admin Center to check the mailbox storage quota for a user and, if possible, set the limit to a higher number.
Setting Mailbox Size Limit for a Single User
- Connect to Exchange Online using Remote PowerShell.
- 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 KB, MB, or GB. See the below example to set the mailbox limit to 30 GB for a single user.
Set-Mailbox TestUser@testdomain.com -ProhibitSendQuota 29GB -ProhibitSendReceiveQuota 30GB -IssueWarningQuota 28GB
- 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.
- Connect to Exchange Online using remote PowerShell.
- Once connected, run the PowerShell command below to set the mailbox size limit.
Get-Mailbox | Set-Mailbox -ProhibitSendQuota < Value > -ProhibitSendReceiveQuota < Value > -IssueWarningQuota < Value >
You can apply filters to the Get-Mailbox cmdlet or to Get-User cmdlet to control the users for whom you’re applying these changes. Below is an example to filter the command to the sales department of an organization.
Get-User | where {$_.Department -eq “Sales”} | Get-Mailbox | Set-Mailbox -ProhibitSendQuota < Value > -ProhibitSendReceiveQuota < Value > -IssueWarningQuota < Value >
Using the above command, you can easily set the mailbox size limit for multiple users. After setting the mailbox size limit, you’ll not receive the ‘mailbox size limit exceeded’ warning.
Method 2: Archive Mailboxes
If there is no room to increase the mailbox size limit, or you still see the same warning after changing the limit, then it means your Office 365 subscription storage quota is full. So, you’ll have to empty the mailboxes or other folders.
In such cases, deleting the mailbox data is not an option, as it contains crucial information about a user or organization. A safer option is to archive or backup Office 365 mailboxes to the local system and then remove the backed-up mailboxes from the server.
Bulk Backup Office 365 Mailboxes Securely
For a limited number of users, you can either use Outlook or Office 365 eDiscovery to export mailboxes to PST. But if you need to back up multiple mailboxes simultaneously, using a professional backup tool will save you time.
You can use the Kernel Export Office 365 Mailbox to PST tool to back up the primary, shared, archive mailboxes, public folders, and groups to PST. The tool allows you to download the mailboxes of multiple users in one go and offers several filters to customize the backup.
Using this software, you can quickly back up your Office 365 mailboxes and free up storage in the Office 365 account to get rid of the “mailbox size limit” warning.
Tips to Avoid Office 365 Mailbox Size Warning
After fixing the mailbox quota warning message O365, follow these points to make sure you do not get the warning again.
- Set up Auto-Archiving: Office 365 allows you to archive emails or mailboxes. You can enable the archiving from Exchange Admin Center or use Outlook to configure the auto-archiving. This will automatically create free space in your primary mailbox.
- Manual Mailbox Cleanup: You can also manually view and find obsolete data items from the mailbox. Then, remove the data from the mailbox and also from the Deleted Items folder. Remember that deleting emails will not immediately create free space. The deleted mail will stay on the server as per the data retention policy.
- Upgrade the Plan: Another option worth exploring is upgrading your current Office 365 plan. For large organizations, choosing a plan that offers more storage capacity is a more logical choice than manual data cleanup.
Additionally, if your organization allows, use an Exchange reporting tool to get instant update about the size of user mailboxes. This will simplify storage management.
Conclusion
The Office 365 mailbox size warning is a common Office 365 problem that requires an urgent solution. Increase the mailbox size limit if possible. Otherwise, you must remove data from the mailbox. For exporting data of several users simultaneously, use the Kernel Export Office 365 Mailbox to PST. You can test the tool for free with the trial version to save up to 10 items per folder.
Frequently Asked Questions
Ans: When the storage quota of your mailbox has reached a predefined threshold value, say 90% of your total limit; Exchange sends you a warning to notify you regarding the space. So, you can manage the size before the storage capacity reaches 100%.
Ans: Open Outlook, configured with your Office 365 user account. Click the File option from the menu. In the Info section, click on Tools and choose the Mailbox Cleanup option. Finally, click the View Mailbox Size button. It will list all the folders in your mailbox along with the size.
Ans: There are three ways to increase your mailbox storage and avoid getting the mailbox quota warning message in O365:
1. Upgrade to a plan that offers 100 GB storage capacity.
2. Buy extra storage if eligible.
3. Enable and use the archive mailbox.
