Increase Office 365 Mailbox Size to 100 GB – Free Ways

Updated On - October 24, 2023 by Henry Bray |

Reading Time: 5 minutes

Have you hit the storage limit for your Office 365 mailbox and are looking for a solution to increase Office 365 mailbox size? The first step is to see if an additional mailbox can be added to your Office 365 subscription at the current price.

Below is a table comparing the 50GB and 100GB mailbox sizes available with various Microsoft Office 365 plans.

We still have a couple of choices if you’ve hit the ceiling of your plan. The email can be transferred to the Online Archive or changed to a different Office 365 plan.

Office 365 storage limits

Before 2013, Microsoft raised the mailbox limit for the E3 and E5 plans and did so again later. You may still be using the lower 25GB limit for Exchange Online plan 1 and the lower 50GB limit for Exchange Online plan 2 if your mailboxes were created before 2016.

Even after upgrading to a higher Office 365 plan—E3, for instance—the mailboxes may still be limited to a smaller size.

Or, you can also use PowerShell:

  • 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

What Happens When a Mailbox Size Limit Is Reached?

The warning limit, the send limit, and the send/receive limit all depend on the mailbox storage quotas that have been set up. When a user reaches one of these thresholds, they will receive an alert.

  • If a user’s Office 365 email storage quota is about to be reached, a warning limit will be displayed to encourage the deletion of less important messages. Email sending is disabled if storage space is not made available.
  • Users can no longer send emails due to a limit on the number of messages they can send. Getting rid of old emails from the inbox should resolve the problem. Email delivery is still possible.
  • Email storage is at capacity, and the user can send or receive messages once space is available. The sender receives a non-delivery report (NDR).

Methods to Increase Office 365 Mailbox Size

Users of Office 365 have access to several options for expanding their mailbox capacity, each of which has its own set of requirements. Otherwise, you’ll need to delete or archive old messages to make room in your inbox. Below are some solutions to common Office 365 email storage problems.

Upgrade the Subscription

Increasing the subscription plan is a simple but costly option. Mailbox quotas on Exchange Online can be increased with a more expensive Microsoft Office 365 subscription.

Edit Quota

Mailbox quotas, as well as the warning limit, transmit limit, and receive limit, can be modified by administrators. However, these figures must be within those allowed by the current Office 365 plan. By default, Office 365 sets the warning quota at 98% of the maximum mailbox size, the send quota at 99%, and the send/receive quota at 100%. Centrally, Office 365 administrators can adjust user mailbox quotas.

Enable archiving

Depending on your needs, you can enable either 50 or 100 GB of extra cloud storage capacity for email by activating the Mailbox archive. A single user can access as much as 1.5 terabytes of archive storage with the highest tier of membership options. When the first 100 GB of archive storage in Office 365 is exhausted, an additional 100 GB of cloud-based archive space is made available. The term “auto-expanding” describes this function. The mailbox archive is only for the user’s personal use. For instance, archiving other users’ emails is strictly forbidden. Data from the archive mailbox is kept only in the cloud, while data from the primary mailbox can be kept in both the cloud and an email client.

Delete Unnecessary Data

You can clear up space in your inbox by deleting old messages you no longer require. Microsoft Office 365 users can download their email messages to their computer, create a local copy, and permanently delete the originals from the cloud storage.

Keep in mind that if you delete an email in your email client (like Microsoft Office Outlook), you should double-check to see if it was also removed in the cloud by using Outlook Online.

Expand your Office 365 mailbox

If the subscription allows, Office 365 administrators can raise the mailbox size via PowerShell. Suppose the user’s mailbox is still subject to the previous Office 365 mailbox size limit, despite Microsoft increasing that limit for the user’s subscription plan. In that case, this approach can be employed (for example, the limit was increased in 2013 and 2016 for Office 365 E3 and E5 subscription plans). If you set up your Office 365 mailbox before 2016, you can use this method to expand its storage capacity from 25 GB to 50 GB or from 50 GB to 100 GB, depending on your current plan.

Note: Increasing the maximum mailbox size will not affect other constraints, such as the size of individual emails, the size of address books, the number of folders in your mailbox, the number of messages you may send at once, etc.

How to Increase Office 365 Mailbox Size in PowerShell

Although the mailbox size may be viewed in the web interface, expanding an Office 365 mailbox requires using PowerShell. To begin, launch Windows PowerShell with administrative privileges:

  1. Open the Start menu, type “cmd,” right-click the resulting shortcut, and then select Run as Administrator.
  2. Then launch PowerShell and link up with Exchange Online. Performing this action is necessary before running cmdlets for controlling Exchange Online.
  3. Run the following command and enter your Office 365 administrator credentials:

$UserCredential = Get-Credential

  1. log in to Exchange Online again using the same credentials you used before:

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri -Credential $UserCredential -Authentication Basic -AllowRedirection

Import-PSSession $Session -DisableNameChecking

  1. In order to see how much space a person has in their email, use the following command.

Get-Mailbox <User ID> | Select *quota

  1. Now is to execute the command to increase Office 365 mailbox size limit:

Set-Mailbox <UserID> -ProhibitSendQuota <Value> -ProhibitSendReceiveQuota <Value> -IssueWarningQuota <Value>


  • The proper storage quotas for an Office 365 mailbox are ProhibitSendQuota, ProhibitSendReceiveQuota, and IssueWarningQuota. In order for the two values to be compatible, the ProhibitSendQuota must be less than or equal to the ProhibitSendReceiveQuota. The ProhibitSendQuota value must be more than or equal to the IssueWarningQuota value.
  • <UserID> is the user’s email address in Office 365, user principal name, or globally unique identifier (GUID).
  • The storage capacity, expressed in gigabytes, megabytes, or kilobytes, is denoted by the< Value> (GB, MB, or KB).

It is possible to reduce the default value of the IssueWarningQuota to provide users with advanced warnings before they reach the limit on their mailbox’s free storage space.

Below is an example of the command that is used in this instance:

Set-Mailbox -ProhibitSendQuota 98GB -ProhibitSendReceiveQuota 99GB -IssueWarningQuota 96GB

Please be aware that this command can only increase Office 365 mailbox size if it is supported by the license (subscription plan).


You can now use PowerShell to audit your organization’s Office 365 mailboxes and adjust storage quotas when necessary. Verify that your settings are accurate to prevent accidental deletion of messages. It is recommended to take advantage of free Office 365 backup solution before deleting any mailbox items to keep mailbox growth under control.

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Author: Henry Bray

Henry Bray is a young technologist and content a Content Writer at Regain Software, loves to write about MS Outlook, MS Exchange Server, Office 365, Mozilla Thunderbird and many more email applications.

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