Is your Office 365 mailbox full? This is a common occurrence for busy individuals who receive thousands of emails on a regular basis.
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. They can’t just go on and hit delete all as this will also remove any important mail. Don’t worry 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 as 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): Login to Admin console, go to “Billing” -> “Your products” to see all licenses and subscriptions.
Outlook Web App: Log in to Outlook web portal, click the profile icon, go to “My Microsoft account page” and look for “Subscriptions”.
Office Desktop App: Open any Office app (Word, Excel, etc.), go to “File” -> “Account”, and check “Product Information”.
Then take a 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.
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: 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.
As text itself doesn’t take up much space, but if you combine high-resolution images, PDFs with tons of pages, or other hefty attachments, then your emails will swell up and take up more space.
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: In the Microsoft 365 Admin Center (Compliance > Information Governance > Archive), enable archiving for the desired user’s mailbox.
- Set Retention Policies: In the Microsoft 365 Admin Center (Compliance > Information Governance > Retention policies), 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 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.
Save Emails Professionally and Clear Out Office 365 Mailbox Full Error
One of the easiest ways to get back the space is to delete the already existing mail. However, the historical emails contain a lot of critical data so a blind deletion is out of the question.
Moreover, purchasing an archive license adds another perpetual cost on top of the regular M365 license. Instead what admins can do is make a one time investment into a unique backup solution. Use it to make an offline copy of files and then delete those files from the cloud.
The solution we propose is the SysTools Backup and Restore tool.
Step 1. Install a copy of the software on your workstation then select a mode (Admin for organization-wide backup/User for a specific account)
The steps vary slightly depending on the mode you choose so follow accordingly. We have highlighted the steps that differ to make it easier for you.
| Steps | Admin Mode | User Mode |
| 2 | Select (Microsoft 365) as the source and (Outlook) as the destination, then select emails in workloads. Apply date filters for time-sensitive backups | In the current version source (M365) and destination (Outlook for PST) are fixed; tick the checkbox next to the email workload. Add date filters if need be. |
| 3 | Perform Validation of Admin & Application ID. | Log in with User Microsoft 365 credentials, accept permissions, & validate. |
| 4 | Select file path, size, and validate. | Set a backup folder path, and size limits, and validate. |
| 5 | Add users via fetch, import, or download option | Fetch, view, & select folders for calendar workload |
| 6 | Preview, select, set priorities, and validate accounts. Then hit Start Backup. | Start the backup by pressing the designated button. |
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.