What Are My Mailbox Size Concerns with Office 365?

Businessman and his administrator doing a routine check on their organization's computers - checking their Office 365 mailbox size.

Be sure your admin is checking your organization’s mailbox sizes regularly.

Microsoft Office 365 offers a variety of features to its users, but one feature that is often overlooked until it becomes a problem is mailbox size. Whether you are running a small business or a personal email account, having the right-sized mailbox is critical to ensure that email messages are delivered on time and without any issues.

Many people start using Office 365 with a small mailbox and then realize their mailbox has become too full. At that point, it cannot be easy to find out how to increase your mailbox size in Office 365.

So, what are your mailbox size concerns? Here we explore and explain some of the common questions around Microsoft Office 365 mailbox size.

How Do You Check Mailbox Size in Office 365?

Office 365 only offers a limited amount of storage space. However, the default size varies according to the subscription pack you choose and the type of mailbox. While some default sizes are 50GB, others are 100GB.

As you can see, it is a limited space that sooner, might not be able to serve your needs anymore. And that’s why it is good for your admin to regularly check the mailbox size to avoid issues like the inability to send and receive messages.

However, the Office 365 Admin Center does not provide any tools to manage mailbox sizes, including your own. Office 365 natively uses Microsoft Exchange Online, which allows you to manage user mailbox sizes.

To get the usage report from the Microsoft 365 Admin center, here’s how to go about it:

  • Go to Microsoft 365 Admin Center
  • Click on the Reports tab, then Usage and select Report
  • Go to Exchange, and there you get the Mailbox Usage

So, the Mailbox Usage report you get from the Admin Center will indicate the consumed storage space. Luckily, you can still access the real user mailbox size, shared mailbox size, and resource mailbox usage report via the Exchange Admin Center (EAC) or Exchange Online via the Other Exchange Reports in the left pane.

And this is how to view the actual Mailbox size report:

  • Login to Microsoft 365 Manager Plus.
  • Click the Reports tab.
  • Traverse to Exchange Online, then the mailbox Reports in the left window.
  • Within the Size Reports group, tap on Mailbox Size report.
Can I Increase My Office 365 Mailbox Size?

Yes, you can. Any user can increase their mailbox size in these two ways:

  • You can allot it an Exchange Online Plan 2 license to augment the storage limit from 50GB to 100GB.
  • Allow Exchange Online Archiving. You will get an extra 50GB of space, and with the auto-expanding archiving, you can get even unlimited space, but it’s contingent on your Microsoft 365 license.

Growing your mailbox to your maximum share isn’t the only way to make your mailbox space. Also, Exchange Online lets you use retention policies to keep or do away with data automatically, depending on the criteria you select.

There are also backup and archiving tools available online to decrease the data stored in your cloud. These tools allow you to preserve data discoverability and hinder the mailbox from congestion.

How does Archiving Operate?

There are two ways to archive:

  • By creating an archiving policy. The policy operates by retention, where the old data is automatically archived or depending on the retention tags your company allocates data.
  • Sending the items yourself (manually).

The plan you choose will determine how much storage space you have per mailbox and the other features you will receive. Each plan also allows archiving mailboxes, which hold emails that are no longer in daily use but still needed for reference.

Archiving is charged based on storage size, so it is good to look at cheaper plans if you’re not expecting your employees to need more space.


Office 365 is a very capable email server. Users with larger mailbox sizes may want to take a moment to consider their storage options with Office 365. Smaller mailbox sizes may be more than sufficient for their needs.

You can do most things on it on Exchange, such as auto-responders, archiving, and other capabilities. And Microsoft has found workarounds to make it possible for even those with mailboxes over the threshold. As long as you’re willing to be cautious about some of the issues surrounding this solution, your organization can use Office 365 and have mailboxes upwards of 25 GB.

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