Manage Exchange Online Mailbox Sizes & Limits: A 2026 Guide

Read time: 15 minutes

A full Exchange Online mailbox can do more than trigger a storage warning. It can stop users from sending or receiving new messages.So, to fix it, you first need to clearly understand mailbox quotas, when to clean up data, adjust limits, or consider archiving options.

The exact Exchange Online mailbox size limit depends on mailbox type and Microsoft 365 subscription plans. Also, the assigned Microsoft 365 license determines the storage availability.

Here, we will explain the current Microsoft 365 mailbox size limits, how to check mailbox usage, and practical ways to manage Exchange Online mailboxes.

Know Size Limits: Exchange Online Storage by Mailbox Type

Exchange Online limits depend on the Microsoft 365 subscription plans and mailbox type. You can check the table below to see the mailbox limits provided by Microsoft.

Mailbox Type	Microsoft 365 Basic and Standard	Microsoft 365 Business Premium	Microsoft 365 Enterprise E3/E5	Office 365 Enterprise E1	Office 365 Enterprise E3/E5	Office 365 Enterprise F3
User mailboxes	100 GB	100 GB	100 GB	50 GB	100 GB	2 GB
Archive mailboxes	50 GB	1.5 TB	1.5 TB	50 GB	1.5 TB	Not available
Shared mailboxes	50 GB	50 GB	50/100 GB	50 GB	50/100 GB	50 GB
Resource mailboxes	50 GB	50 GB	50 GB	50 GB	50 GB	50 GB
Public Folder mailboxes	100 GB	100 GB	100 GB	100 GB	100 GB	100 GB
Group mailboxes	50 GB	50 GB	50 GB	50 GB	50 GB	50 GB

How to Check Exchange Online Mailbox Limit Usage?

You can check Exchange Online mailbox usage with the help of New Outlook/OWA, Exchange Admin Center (EAC), and PowerShell commands. Here are complete steps to check Office 365 mailbox size limit usage for all of them.

Method 1. Use New Outlook or OWA to Check Mailbox Usage

Follow the given steps to check the Exchange Online mailbox storage usage directly from Outlook.

Step 1. Launch Outlook and go to File > Settings. Go to Outlook and go to file then settings

Step 2. Navigate to Account section and proceed to Storage.

Step 3. Review the total storage usage.

Step 4. Scroll down to check the consumed space of each mailbox folder separately. Check mailbox folder storage

Note: All the above steps are the same for Outlook Web Access (OWA).

Method 2. Inspect Office 365 Mailbox Usage In Microsoft Admin Center

Here are the detailed steps to track organization-wide Microsoft Exchange Online mailbox limit usage:

Step 1. Log in to Microsoft 365 admin center.

Step 2. Expand the Reports section and go to Usage.

Step 3. Navigate to Mailbox usage tab for a storage overview.

Note: Click on Export option beside Storage to get the detailed report in CSV format.

go to mailbox usage and click on export for csv format

Step 4. Scroll down to check the mailbox’s current Quota status. check the mailbox quota status

Method 3. Verify Individual Mailbox Usage With Exchange Admin Center

Administrators can inspect the Microsoft 365 mailboxes in EAC using the following steps:

Step 1. Go to the Exchange admin center.

Step 2. Expand Recipients and click on Mailboxes.

Step 3. Select the mailbox and click on it.

Step 4. Locate the General tab and scroll down to view the Mailbox Usage limit. View the mailbox usage limit

Step 5. Then, go to Mailbox section to inspect the Message size restriction. Check the message size restriction

Method 4. Examine Office 365 Mailbox Usage With PowerShell Commands

You can also use PowerShell Commands to identify folders such as Inbox, Sent Items, Deleted Items, or Recoverable Items that consume unusually large amounts of space. Here’s how:

Note: You need the Exchange Online PowerShell module (via Install-Module -Name ExchangeOnlineManagement -Scope CurrentUser) and an administrator account to view mailbox statistics.

Step 1. Execute the command below to connect to Exchange Online PowerShell.

Connect-ExchangeOnline -UserPrincipalName admin@contoso.com

Step 2. Use the command below to check the signal mailbox usage.

Get-EXOMailboxStatistics -Identity user@contoso.com | Select-Object DisplayName, TotalItemSize, ItemCount

Step 3. You can also verify the individual folders like Inbox, Sent Items, and others, using the provided command.

Get-EXOMailboxFolderStatistics -Identity user@domain.com

Step 4. Run the following command to inspect the archive mailbox.

Get-EXOMailboxStatistics -Identity user@contoso.com -Archive

Step 5. Check all mailbox usage at once using the given command.

Get-EXOMailbox -ResultSize Unlimited | Get-EXOMailboxStatistics | Select-Object DisplayName, TotalItemSize, ItemCount

Step 6. Export the report to a CSV file with this command.

Get-EXOMailbox -ResultSize Unlimited | Get-EXOMailboxStatistics | Select-Object DisplayName, ItemCount, TotalItemSize | Export-Csv C:\Reports\MailboxSizes.csv -NoTypeInformation

Manual Ways to Manage Exchange Online Mailbox Sizes & Limits

To manage Exchange Online mailbox size, first check your mailbox and folder-wise storage usage. Delete unnecessary large messages, review Sent Items and Deleted Items, move important older emails to Online Archive, and investigate Recoverable Items if storage remains full. You can also use Exchange Online PowerShell and archive policies to manage mailbox growth.

Method 1. Enable Mailbox Archiving & Set Retention Policies

Here are the steps to manage older email messages with mailbox archiving and retention policies.

For Online Archive:

Step 1. Go to Exchange admin center > Recipients > Mailboxes.

Step 2. Click on the user mailbox that you want to archive.

Step 3. Navigate to Others section to Manage mailbox archive. go to other and then Manage mailbox archive

Step 4. Enable mailbox archiving, provide a Name and click Save. Enable mailbox archiving then give a Name and click Save

Note: You need an Exchange Online Plan 2 or Archiving license to enable it for each user’s mailbox.

For Auto-Expanding Archive

Important to Know:

You cannot turn on Auto-Expanding Archive after enabling it.
It takes up to 30 days to provision an additional license.
Microsoft requires an organization-wide command for hybrid environments.
You need Global Administrator, Organization Management, and Mail Recipients permissions for the steps below.

Step 1. Open PowerShell and connect to Exchange Online with the command.

Install-Module ExchangeOnlineManagement -Scope CurrentUser

Step 2. Run the following commands to enable auto-expanding archiving for the entire organization or specific user mailboxes.

Organization-Wide:

Set-OrganizationConfig -AutoExpandingArchive

Specific user mailbox:

Enable-Mailbox user@yourdomain.com -AutoExpandingArchive

Note: You need to enable archiving before you expand auto-archiving for specific user mailboxes.

Step 3. Review the organization settings or individual user mailbox settings with these commands.

To check organization settings

Get-OrganizationConfig | Format-List AutoExpandingArchiveEnabled

To check specific user mailbox settings

Get-Mailbox user@yourdomain.com | Format-List ArchiveStatus,AutoExpandingArchiveEnabled

Step 4. Once completed, disconnect from Exchange Online.

-ExchangeOnline -Confirm:$false

For Retention Policies

Note: You can set new retention policies or change the existing ones to manage your mailboxes. Here, we are setting a new one.

Step 1. Access the Microsoft Purview portal to continue. Go to Microsoft Purview portal

Step 2. Click on Solutions and proceed with Data Lifecycle Management. Click on Solutions and go to Data Lifecycle Management

Step 3. Navigate to Policies > Retention policies.

Step 4. Create a New retention policy to begin. Create a new retention policy

Step 5. Enter the Name & Description and click Next. Enter the Name and Description and click next

Step 6. Choose between Adaptive or Static type and tap Next. Choose Adaptive or Static type and tap next

Step 7. Turn On the toggle for Exchange mailboxes and click Next. Turn On the toggle for Exchange mailboxes and click Next

Step 8. Retain, archive, or delete data as needed. Then, proceed to Next. Retain archive or delete data and click next

Step 9. Review the created policy and click Submit to apply. review policy and click on submit

Method 2. Manage Message Sizes and Restrictions

Follow the given steps to manage mailbox sizes and restrictions.

To manage message size

Step 1. Go to Exchange admin center > Recipients > Mailboxes.

Step 2. Select the required mailbox to proceed.

Step 3. Locate the Mailbox tab and click on Manage message size restriction. click on Manage message size restriction

Step 4. Set the Message size restrictions as needed and click Save. Set the Message size restrictions and click save

To manage message delivery restrictions

Step 1. Navigate to Mailbox > Manage message delivery restriction. go to mailbox and the Manage message delivery restriction

Step 2. Choose the applicable settings and click Save. choose desired setting and save

Method 3. Customize Mailbox Quotas Using PowerShell

To customize Exchange Online mailbox sizes using PowerShell, execute the steps below:

Note: Exchange Online mailbox quota settings depend on the user’s license, mailbox type, and applicable service limits. PowerShell can configure quota values within the limits supported by the mailbox only.

Step 1. Exchange Online uses three main quota thresholds to control mailbox storage. They should be configured in ascending order.

IssueWarningQuota
ProhibitSendQuota
ProhibitSendReceiveQuota

Step 2. Connect to Exchange Online with the command below.

Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline -UserPrincipalName admin@yourdomain.com

Step 3. Run the command below to check the current quota settings for the user mailbox.

Get-Mailbox -Identity user@yourdomain.com |
Format-List DisplayName,PrimarySmtpAddress,UseDatabaseQuotaDefaults,IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota

Step 4. Execute the following command to customize the mailbox size and quota thresholds for specific user mailboxes.

Set-Mailbox -Identity user@yourdomain.com `
-UseDatabaseQuotaDefaults $false `
-IssueWarningQuota 18GB `
-ProhibitSendQuota 19GB `
-ProhibitSendReceiveQuota 20GB

Step 5. Verify the updated mailbox quotas using this command.

Get-Mailbox -Identity user@yourdomain.com |
Format-List IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota

Step 6. You can also customize quotas for all users, department-wise, and selected list mailboxes with these commands:

For all user mailboxes

Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited |
Set-Mailbox -UseDatabaseQuotaDefaults $false `
-IssueWarningQuota 18GB `
-ProhibitSendQuota 19GB `
-ProhibitSendReceiveQuota 20GB

For department-wise mailboxes

$SalesUsers = Get-User -ResultSize Unlimited `
-Filter “Department -eq ‘Sales'”
$SalesUsers | ForEach-Object {
Set-Mailbox -Identity $_.UserPrincipalName `
-UseDatabaseQuotaDefaults $false `
-IssueWarningQuota 18GB `
-ProhibitSendQuota 19GB `
-ProhibitSendReceiveQuota 20GB

For the selected list of mailboxes

$Mailboxes = Get-Content “C:\Temp\MailboxList.txt”
$Mailboxes | ForEach-Object {
Set-Mailbox -Identity $_ `
-UseDatabaseQuotaDefaults $false `
-IssueWarningQuota 18GB `
-ProhibitSendQuota 19GB `
-ProhibitSendReceiveQuota 20GB

Step 7. Check the applied quotas for all users, department-wise, or selected mailboxes; run the given commands.

To check all user mailboxes

Get-Mailbox -RecipientTypeDetails UserMailbox -ResultSize Unlimited |
Format-Table DisplayName,PrimarySmtpAddress,IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota -AutoSize

To check department-wise mailboxes

Get-User -Filter “Department -eq ‘Sales'” -ResultSize Unlimited |
ForEach-Object {
Get-Mailbox -Identity $_.UserPrincipalName -ErrorAction SilentlyContinue
} |
Format-Table DisplayName,PrimarySmtpAddress,IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota -AutoSize

To check selected mailboxes

$userList = @(
“user1@yourdomain.com”,
“user2@yourdomain.com”,
“user3@yourdomain.com”
)
foreach ($user in $userList) {
Get-Mailbox -Identity $user |
Format-List DisplayName,IssueWarningQuota,ProhibitSendQuota,ProhibitSendReceiveQuota

Step 8. Disconnect from Exchange Online once you check the applied settings.

Disconnect-ExchangeOnline -Confirm:$false

Method 4. Upgrade Your Current Microsoft 365 Plans or Licenses.

If your mailbox needs more storage, consider upgrading to a plan with a higher mailbox limit. Alternatively, add Exchange Online Archiving to an eligible Plan 1 subscription to increase archive storage and enable auto-expanding archiving. Check the Microsoft 365 subscription plans for eligibility and limits.

Method 5. Manage Exchange Mailboxes Using Outlook At the User Level

Here are the steps to clean up mailboxes, sweep unwanted emails, or save large attachments to OneDrive.

To Clean Up Mailboxes

Step 1. Launch Outlook and click on File > Settings.

Step 2. Navigate to Accounts > Storage > Manage storage.

Note: Make sure to select an Exchange account first.

Step 3. Select the mailbox folder and use the Empty dropdown to delete older items. empty mailbox folder in new outlook

Step 4. Confirm the delete action by clicking OK. Click on ok to delete

Step 5. It will start emptying the mailbox folder.

To Sweep Unwanted Emails

Step 1. Select the email messages and click the Sweep option. select email messages and click on sweep

Step 2. Choose the applicable option and click OK.

Step 3. It will start the process based on the selected action.

To Save Large Attachments to OneDrive

Step 1. Access the required mailbox folders to Sort emails.

Step 2. Sort email messages using the Size and Largest on top filters. Sort email messages using filters

Step 3. Open the email messages and click on the down arrow.

Step 4. Choose the Save to OneDrive option. choose the save to drive option

Step 5. Do this for all email messages that contain large attachments.

Step 6. It will save the attachments to OneDrive and help you manage mailbox size.

Also Read: How to Increase Office 365 Mailbox Size to 100GB ?

Do You Want to Keep Mailbox Data Without Consuming Mailbox Storage or upgrading license?

Backing up mailboxes is one of the best ways to manage Exchange Online mailboxes. You can use the eDiscovery tool offered by Microsoft or direct solutions like Kernel Office 365 Backup and Restore tool to backup Exchange Online Mailboxes . The native solutions will be suitable for technical users and, the automated solutions help those users who want to simplify the entire process.

Let’s Recap

Here, we have covered a detailed guide on how to manage Exchange Online mailbox sizes and limits. You can use the provided information to know the Office 365 mailbox limits, check the usage, and use practical ways to manage them.

However, if you want to keep your mailbox data for a longer period, then backing it up is the recommended solution. For this, you can use Microsoft’s native export solution or the suggested one based on your requirements.