How to Increase Mailbox Size in Office 365

Have you reached your Office 365 mailbox size limit and want to know how to increase it? Then we first have to check if you can increase the mailbox within your current Office 365 plan.

Depending on your Microsoft Office 365 plan you can have either a 50GB or a 100GB mailbox size. If you have reached the limit within your plan, then we still have two options. We can either move the mail to the Online Archive or in some cases switch over to a different Office 365 subscription.

In this article, we are going to take a look at the default mailbox sizes in Office 365 and how to increase them.

Office 365 Mailbox Size

Before we are going to take a look at how to increase the mailbox size, let’s first check what the maximum size is in your Microsoft 365 plan:

Microsoft Office 365 PlanExchange
Online Plan
Mailbox sizeOnline Archive size
Microsoft 365 Business BasicPlan 150GB50GB
Microsoft 365 Business StandardPlan 150GB50GB
Microsoft 365 Business PremiumPlan 150GB1.5TB1
Office 365 F3Kiosk2GBAdd-on
Office 365 E1Plan 150GB50GB
Office 365 E3Plan 2100GB1.5TB1
Office 365 E5Plan 2100GB1.5TB1
Microsoft 365 F3Kiosk2GBAdd-on
Microsoft 365 E3Plan 1100GB1.5TB1
Microsoft 365 E5Plan 1100GB1.5TB1

1 The initial archive size is 100GB. When auto-expanding is turned on, the archive will incrementally increase to the max of 1.5TB.

Microsoft has increased in the mailbox limitation in the past, in 2013 and later again for the E3 and E5 plans. So if your mailboxes were created before 2016 then it’s possible that your mailboxes still have the old limits, 25Gb instead of 50Gb for Exchange Online plan 1 and 50Gb instead of 100Gb for plan 2.

Also when you have upgraded your Office 365 plan to E3, for example, then the mailboxes may still have the old mailbox size limit.

Checking the current max size

So it’s possible that your mailbox is still assigned an old limit. If that is the case, then we can easily increase the limit of the mailbox within the current plan. We can check the current mailbox size of a mailbox in the Exchange Admin Center:

  1. Open the Exchange Admin Center
  2. Expand Recipients and open Mailboxes
  3. Select the mailbox
  4. Scroll a bit down the view the mailbox size
increase mailbox size office 365

We can also use PowerShell to get the mailbox size. Make sure that you have installed the PowerShell Exchange Online Module. We still need to use the old Get-Mailbox cmdlet to view the mailbox limits:

# Connect to Exchange Online
Connect-Exchangeonline -userprincipalname

# Get the mailbox size limits
Get-Mailbox -identity | select IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota

# Get all mailbox sizes
Get-Mailbox | select DisplayName, IssueWarningQuota, ProhibitSendQuota, ProhibitSendReceiveQuota


I have also created a PowerShell script that exports all mailbox sizes to Excel. This way you can easily identify mailboxes that still have old limits or mailboxes that are about the run out of space.

Increase Mailbox size Office 365 with PowerShell

Increasing the mailbox size can only be done with PowerShell. You will need to have the Exchange Online Module installed before you can connect to Exchange Online with PowerShell.

We need to set 3 values:

  • IssueWarningQuota – When the warning is displayed in Outlook
  • ProhibitSendQuota Determines when the user can’t send mail anymore
  • ProhibitSendReceiveQuota The user can’t send or receive mail when reached

You want to give the user a warning on time, not when the mailbox limit is reached. So we set the warning to 95Gb. Then prohibit the sending of new mail at 98Gb, so we still have a little room to receive mail until we reach the limit of 100Gb.

# Connect to Exchange Online
connect-exchangeonline -userprincipalname

# Increase mailbox size
Set-Mailbox -identity -IssueWarningQuota 95GB -ProhibitSendQuota 98GB -ProhibitSendReceiveQuota 99GB

You can also increase all the mailboxes in one command. If all your users have the same licenses then you can simply run the following PowerShell command to increase mailbox size to 100Gb in Office 365.

Get-Mailbox | Set-Mailbox -identity -IssueWarningQuota 95GB -ProhibitSendQuota 98GB -ProhibitSendReceiveQuota 99GB

If you have a large tenant with different Microsoft Office 365 plans for your users then you can’t increase all the mailboxes. You could run the command above, but it will throw a lot of errors for all the mailboxes that can’t be changed.

With the command below we get all the user mailboxes (not the shared) and select the mailboxes that have a ProhibitSendReceiveQuota of 50GB. Also, we need to make sure that the user has an Exchange Online Plan 2 mailbox, which we do with BPOS_S_Enterprise. (BPOS_S_Standard is EO Plan 1)

Get-mailbox -Filter {RecipientTypeDetails -eq "UserMailbox"} | 
Where-Object {($_.ProhibitSendReceiveQuota -eq '50 GB (53,687,091,200 bytes)') -and ($_.PersistedCapabilities -contains "BPOS_S_Enterprise")} | 
Set-mailbox -ProhibitSendQuota 98GB -ProhibitSendReceiveQuota 99GB -IssueWarningQuota 95GB

Increase Shared Mailbox Size

Shared mailboxes are limited to 50 GB in all Microsoft 365 plans. The advantage of a shared mailbox is that you don’t need to assign a license to it, only the user(s) who access it needs to have an Office 365 license that includes an Exchange Online plan.

To increase the shared mailbox, you will need to assign an Exchange Online Plan 2 license to it. This license will increase the mailbox limit to 100 GB. When you created the shared mailbox, a user account is automatically created in Microsoft 365 with the same name as the shared mailbox.

To assign the license, open the Microsoft 365 Admin Center, look up the mailbox user under Active Users, and assign the license to the user.

Enable Office 365 Online Archive

If you have reached the limits of your Office 365 plan then your only option is to start moving the mail older than 2 years to the Online Archive.

We first have to check if the archive is enabled in the Exchange Admin Center. If you open the mailboxes you will see a column with the Archive Status. If the Archive Status is none then we can enable it.

  1. Select the User
  2. Click on Others
  3. Click on Manage Mailbox Archive
  4. Enable the archive
office 365 increase mailbox size 100gb

We can also use PowerShell to enable the Office 365 Online Archive

# Connect to Exchange Online
Connect-ExchangeOnline -userprincipalname

# Enable the mailbox for John Doe
Get-ExoMailbox -Identity | Enable-Mailbox -Archive

If you want to enable the archive for all users then use the following PowerShell cmd:

# Connect to Exchange Online
Connect-ExchangeOnline -userprincipalname

# Enable the Online Archive for all mailboxes
Get-Mailbox -Filter {ArchiveStatus -eq 'none' -and RecipientTypeDetails -eq "UserMailbox"} | Enable-Mailbox -Archive

Retention Tag Policies

We can use retention tag policies (RTP) to move the mail automatically to the archive. By default, there should be an RTP that archives all the mail older than 2 years to the archive.

You can change the policy in the Microsoft Compliance Center (Microsoft Purview):

  1. Expand Data lifecycle management
  2. Open Exchange (legacy)
  3. View or edit the Default MRM Policy

The policy should include a retention tag that moves mail to archive after 2 years:

move archived mail policy

Retention Tags are assigned to a Retention Policy, which is again assigned to a mailbox. The default retention policy is always assigned to a mailbox if no other policy is assigned. If you want to change the policy then it’s recommended to create a new Retention Policy.

Frequently Asked Questions

What is the Exchange Online plan 1 mailbox size?

The Exchange Online Plan 1 mailbox is 50GB and the size of the online archive is also 50Gb

What is the Exchange Online plan 2 mailbox size?

The Exchange Online Plan 2 mailbox is 100GB and the size of the online archive is by default 100GB and can be increased to 1.5TB

What is the Exchange Online Kiosk mailbox size?

Kiosk mailboxes are only 2GB and don’t come with an online archive. It’s possible to buy the online archive as an add-on.

Can you increase the Office 365 mailbox size over 100GB

No, you will have to use the online archive for this.

Wrapping Up

Increasing the mailbox size in Office 365 only solves the problem temporarily (or for a couple of years). At the moment you can’t go beyond the 100GB for a mailbox, so make sure you have the archive mailboxes enabled and retention policies that move the mail after 2 years to the archive.

Another good way to limit the growth of mailboxes is to train your users to share links to documents instead of attaching the document.

If you have any questions, just drop a comment below.

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4 thoughts on “How to Increase Mailbox Size in Office 365”

  1. Thank you Rudy!
    This was exactly what i needed to understand, search for and adjust the mailboxes to the correct size.
    I had to add -ResultSize Unlimited, when investigating, as the default limit is 1000

  2. What is the Exchange Online plan 1 mailbox size
    The Exchange Online Plan 1 mailbox is 50GB and the size of the online archive is 100Gb

    The table says otherwise. In my understanding, mailbox size + archive can be 50GB overall, not 50 + 50 as the table says.
    So… three opinions 🙂 What’s correct?

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