Office 365 Mailbox Full? Learn Ways to Get Back Storage

Are you someone struggling with a Office 365 mailbox full? Tired of regularly deleting emails mails only to see your inbox get filed again. You are not alone this common issue for many other users like you that receive numerous emails daily. This guide explores various strategies, from auto-archiving to professional backups, helping you reclaim space and maintain a clutter-free mailbox.

Like you I was also struggling with an Office 365 mailbox that never seem to have enough space. Nevertheless, I was able to successfully solve the issue and will share the knowledge so you could free up some space as well.

O365 mailboxes becoming almost full is a fairly common occurrence for busy individuals. This is because they receive thousands of emails on a regular basis. Moreover, not allocating more space to your inbox can freeze all email communication. So it’s vital that you act on time to prevent this from happening.

The main challenge users face is which approach to use since there are so many pathways to regain mailbox depth. Plus, they can’t just go on and hit “delete all“, as this will also remove any important mail that they didn’t wanted to get rid of. Fret not as we have put together a mix of strategies that can be used in many different scenarios.

We will help you figure out the best way to reclaim the mailbox space and reduce clutter. Let us first start by exploring what are the limits of the M365 mailbox in different business plans. It will help us understand why the problem occurs and how to manage it in the future.

Storage Limits of Various Office 365 Mailbox Plans

Use these Steps to see your current plan:

Microsoft 365 Admin Center (for admins):

Step 1. Log in to the Admin console, go to “Billing”

Step 2.  “Your products” to see all licenses and subscriptions.

Outlook Web App:

Step 1. Log in to the Outlook web portal, and click the profile icon.

Step 2. Then, click on View account.

Step 3. Go to “My Microsoft account page” and look for “Subscriptions“.

Office Desktop App:

Step 1. Open any Office app (Word, Excel, etc.),

Step 2. Go to “File” -> “Account“, and check “Product Information“.

Then look at the list below for the upper limit of data that can be kept in your account.

Plan	User Mailbox Limit	Archive Mailbox Limit
Microsoft 365 F1	2 GB	Not available
Microsoft 365 F3	2 GB	Not available
Microsoft 365 Business Basic	50 GB	50 GB
Microsoft 365 Business Standard	50 GB	50 GB
Microsoft 365 Business Premium	50 GB	1.5 TB (with auto-expanding archiving)
Microsoft 365 E1	50 GB	50 GB
Microsoft 365 E3	100 GB	1.5 TB (with auto-expanding archiving)
Microsoft 365 E5	100 GB	1.5 TB (with auto-expanding archiving)
Office 365 E1	50 GB	50 GB
Office 365 E3	100 GB	1.5 TB (with auto-expanding archiving)
Office 365 E5	100 GB	1.5 TB (with auto-expanding archiving)
Office 365 F3	2 GB	Not available

Additional Notes:

Auto-Expanding Archiving: For plans with this feature, archive storage starts at 100 GB and can expand up to 1.5 TB.

Shared Mailboxes: Typically limited to 50 GB unless an Exchange Online Plan 2 license is assigned, which increases it to 100 GB.

Public Folder Mailboxes: Can collectively store up to 100 TB, with a limit of 100 GB per individual mailbox.

These are just the default limits Microsoft allows admins to set their custom limit on user mailboxes. If you are a new admin and wish to know if your predecessor has tweaked with the mailbox storage you can use the following PowerShell command.

First, ensure you are connected to Exchange Online PowerShell. If you are not, run this command first:

Connect-ExchangeOnline

Once connected, run the following command to see the storage quota settings for all user mailboxes in your organization:

Get-Mailbox -ResultSize Unlimited | Select-Object DisplayName, UseDatabaseQuotaDefaults, ProhibitSendReceiveQuota, ProhibitSendQuota, IssueWarningQuota

Knowing about these boundaries is the first step. Next, see the actual items that occupy unnecessary space.

What Causes Office 365 Mailbox Full Issue?

The answer is simple: most of the time it is the incoming emails. Receiving too many emails can result in a mismanaged mailbox.

Moreover, the default rate at which M365 clears out spam is 30 days. During this period, the emails in Junk or Soft Deleted folders continue to occupy space in your mailbox.

So, if during a particular cycle you get too many invalid messages that are not permanently removed, you can fill up your mailbox.

Sending and receiving emails with large attachments regularly is another major cause for a premature Office 365 mailbox full error.

Text in an email doesn’t take up much space, but if you receive (or send) high-resolution images, PDFs with tons of pages, or other hefty attachments, then your emails will swell up and take up more space.

This same problem extends to your Calendar, where recurring meetings with the same large attachment are stored over and over again, with each instance consuming more space.

You may have setup some rules that create multiple copies of the same messages in different folders, all of which count towards the storage individually. In addition, your mailbox silently stores data from other connected apps, like chat histories from Microsoft Teams or voicemails with audio files, which also add to the total.

On top of this, when a person leaves your organization, their contact card remains in your personal contacts folder and their old meetings remain on your calendar. These “orphaned” items continue to count towards your mailbox storage.

If you imported a lot of external emails into your account, this sudden increase in the total volume of data in your account may go over the default limit or the limit set by your admin.

Also the only reason why people continue to keep their email boxes full is because they don’t have a clear backup strategy.

Microsoft allows you to expand your initial mailbox storage multiple times its actual limit through a premium service. So, let us see what it is.

Purchase, Enable, and Use Auto Archive Feature

• Get the Right Plan: Purchase Exchange Online Plan 2 via the Microsoft 365 Admin Center (Billing > Purchase services).
• Enable Archiving:
  • Go to Exchange Admin Center
  • Click on the User whose Office 365 Mailbox is full.
  • Switch to the Others Tab in the Use Mailbox Pane.
  • Click on Manage mailbox archive.
    
  • Toggle the Switch to On(Enabled) Position, Type a Name and Save.
• Set Retention Policies: In the Microsoft 365 Purview Portal.
  • Data Lifecycle Management > Policies > Retention Policies > + New Retention Policy
  • Follow the on screen instructions to make your custom Retention Policy that decides what organization data stays and for how long.

Create and configure a retention policy to automatically move emails to the archive based on age or folder. Assign the policy to the relevant mailboxes.

• Access the Archive: The archive mailbox will appear in Outlook (desktop/web) below the primary mailbox. User emails will begin auto-archive as per the retention policy.
• (Optional) Manual Archiving: If users want they can, manually move emails to the archive by right-clicking and selecting Move > Archive. (Ensure that they are using the In place(Online) Archive and not the regular archive folder. The latter won’t free up any space in Outlook.)

The archiving feature works but it still has a upper limit i.e. 1.5 TB you won’t fill it anytime soon but once you do there is no other way out. So you have to move some data offline. Moreover, it is also possible that you maintain a semi local presence without knowing there is a valid query amazon users already in such a situation let us address it before revealing the best method.

Can Shrinking PST Clear an Office 365 Mailbox that is Full?

Those who use the Classic Outlook client often maintain an on premise PST. They can shrink down the size via the compact feature. However this won’t free up any space in the M365 cloud environment. This is because the PST is only present in the local system.

Find and Delete Large Emails to Reduce O365 Mailbox Size

You can use Outlook’s advanced filtering capability:

• In the Inbox toolbar select “All”, put “Sorted: Largest on Top” (Descending order) and order “By Size”.
• Right Click and Delete.
• Repeat for every item you no longer require.

Note this just puts your messages in the Delete folder. If you stop now your Mailbox will continue to face storage issues. Up until Outlook runs the default 30 day permanent removal. However, by that time new mails will arrive so you will be in the same situation. So what you can do right now is clear out the unwanted mail.

Permanently Delete Mails to Get Back Lost Storage in Microsoft 365 Mailbox

You have to empty out two folders.

• First is Junk, This is for emails that are considered spam as per your rules or Outlook’s internal filter.
• Go through the list once and see if there is nothing important select all right click and Delete.

Next go to the Deleted Items folder. This is a temporary space for all unwanted data that automatically clears out every 30 days.

Note this 30 day cycle is not fixed at the folder level but for each individual message, the countdown starts as soon as the message enters the Deleted Items folder (timer resets if message is pulled out of the Deleted folder).

Resolve the O365 Full mailbox issue in the same steps we did for Junk folder i.e. Select All > Right-click and Delete.

Conclusion

Now readers know exactly what to do if the Office 365 Mailbox Full alert pops up while using Outlook. The smart storage management strategies given here can help manage this problem. Moreover, it is not always possible to delete all emails. That is why we also include a backup solution that can preserve all available mail from a particular time period. Admins /users can then safely delete the now backed up emails.