Summary: : OST is the primary file type used by Outlook 365 to maintain a local copy of mailbox data. When this OST file becomes large, users may encounter the “Your mailbox is almost full” error. There are some temporary and permanent solutions mentioned in this post to fix this error and manage your Outlook 365 storage space.
Outlook 365 stores the mailbox data (emails, contacts, calendars, tasks, journals, notes etc.) in the OST file, which has a limit of 50 GB. However, Outlook users start experiencing issues when the OST file grows large and exceeds 10 GB size. These include send/receive errors, slow search results, slow Outlook load time, etc.
When the OST becomes too large and reaches the limit (10 GB, 20 GB or more) set by the administrator, Outlook users start receiving the warning message “your mailbox is almost full.” This is a concerning message that must be fixed to ensure uninterrupted email services and avoid issues, such as Outlook cannot send or receive new messages.
Luckily, there are various ways to overcome the issue of OST file storage space. The most known are the deletion of unwanted messages, clearing junk folders, disabling Cached Exchange Mode, and many others.
What Triggers the Outlook 365 Mailbox Full Error?
Every day hundreds of emails are sent and received by Outlook 365 users, resulting in a shrinking of storage space. In addition to emails, large attachment files are also one of the reasons for receiving the mailbox full error. Therefore, it’s important for you to organize your mailbox in an efficient way to have decent storage space for your Outlook 365 profile.
Below are the main reasons for receiving Outlook 365 mailbox is almost full error:
1. Large Size of OST File
The large size of Outlook OST is one of the reasons for Outlook 365 performance issues. Each Outlook profile is usually given a storage space of up to 50 GB (more in some exceptional cases). When it gets exhausted, the message of a mailbox full error occurs.
2. Deleted Emails
Most of the time, when a user gets irrelevant emails in the inbox, they delete them from the account not noticing the fact they’re going to the deleted items folder. They consume a large storage space resulting in receiving Outlook 365 mailbox full error.
Solutions to Fix Error “Your Mailbox is Almost Full” in Outlook 365
Now, let’s learn the possible ways to fix the mailbox full error.
Solution 1: Archive Mailbox Items
To manage the Outlook 365 storage space, you can archive the older emails. Find the steps below:
- Open Outlook and go to the File tab.
- Select Info > Cleanup Tools > Archive.
- Check the Archive settings and select Archive this folder and all subfolders option.
- Choose the mailbox items you want to archive from your Outlook profile.
- Select the date when you want to archive the older items.
- Click Browse to choose a save location.
- Make sure to mark the “Do not auto-archive” checkbox.
- Hit the OK tab
Solution 2: Remove Oversized Email
The oversized emails and attachments exhaust the Outlook 365 mailbox storage space easily. You can remove the large mail items and attachments by following the given steps:
- Start Outlook 365 and select Search Folders in the folder pane.
- Click on the New Search Folder and select Large Mail option under the Organizing Mail.
- Select mail at least this large and specify the mail size.
- Press OK to finish.
- A new folder of specified size will be created under your Outlook 365 profile. It contains mails larger than specified size automatically.
Solution 3: Use Outlook Clean Up Tool
Make use of Outlook cleaning tool to clear unwanted mails and attachment files from your mailbox. Follow the given steps:
- Select File from the Outlook ribbon.
- Choose the Info option, then go to Tools, and select Mailbox Cleanup
- Set the number of days to find items older than and file size to find items larger than in the mailbox cleanup window.
- Click on Empty tab to permanently remove the delete items folder
Solution 4: Disable Cached Exchange Mode
If Cached Exchange Mode is enabled in the Outlook 365 profile, it will create a local copy of OST files on your computer which results in consuming a hefty amount of storage space. Also, when working with a shared mailbox and Cached Exchange Mode is on, it consumes a lot of storage degrading the email client performance.
In such cases, disable the Cached Exchange Mode to fix the issue:
- Go to the File tab.
- Select the Account Settings profile icon.
- Select the Microsoft or Exchange account and click on the Change option.
- Under the Exchange Account Settings, untick Use Cached Exchange Mode to download email to an Outlook file and leave the
- Restart Outlook.
In these ways, you can manage the Outlook 365 performance and keep on receiving and sending email. Also, users can recreate OST files as a permanent solution to Outlook 365 mailbox full error.
Download Stellar Converter for OST. It comes as a handy solution in the scenario where the OST recreation fails or the OST file becomes inaccessible or orphaned. Also, when the mailbox data is missing after recreating the OST file, you can use the software to restore the missing mail items.
In addition, the software saves OST mailbox oversized attachments separately in a folder and emails in PST file format. This helps reduce the overall file size and prevent chances of corruption or inconsistencies in Outlook data files.
Conclusion
Outlook 365 provides a maximum storage space of 50 GB to its users. Therefore, organizing the mailbox is significant to continue receiving and sending emails. In this post, we have mentioned different ways through which you can take care of Outlook 365 storage space. You can also download and use Stellar Converter for OST to convert the inaccessible mail items from OST to PST files and save attachments separately to reduce overall Outlook data file size. You can also use the software to manage storage space by splitting large OST files into multiple PST files with attachments
