How to Fix Outlook Data File Size Limit and Change Primary Account
Question details
The user needs to manage an Outlook data file that is reaching the 50 GB size limit and wants to understand how to change the primary Exchange account in their Outlook profile.
- Product
- Microsoft Outlook
- Device & OS
- not provided
- Scenario
- Hitting mailbox size limits and needing to reorganize the primary account priority in Microsoft Outlook.
- Observed behavior
- Outlook displays data file size warnings as it nears 50 GB, and the primary Exchange account cannot be switched directly from settings without re-adding the accounts.
Before making changes to your Outlook accounts or compacting data files, ensure you have archived important emails and noted down your account server details and passwords.
Compact the Outlook Data File and Manage Storage
Reduce the size of your Outlook data file by compacting it and adjusting your account synchronization settings.
By default, Outlook.com consumer mailboxes and Outlook data files (.pst and .ost) have a 50 GB limit. If your file is approaching this limit, compacting it can reclaim unused space.
Right-click your account name or data file folder in the Outlook folder pane and select 'Data File Properties'.
Click on the 'Advanced' tab in the properties window, then click the 'Compact Now' button to compress the file and reclaim space.
Go to File > Account Settings > Account Settings. Double-click your account and reduce the 'Mail to keep offline' slider so Outlook downloads only newer mail.
Regularly delete unnecessary emails or use the built-in Archive tool to move older messages into a separate local PST file to stay below the 50 GB limit.
Change the Primary Exchange Account
Outlook assigns the primary Exchange account based on the order they are added. You must remove and re-add them to change this assignment.
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Frequently Asked Questions
What is the maximum size limit for an Outlook data file?
By default, the maximum size for an Outlook data file (.pst or .ost) and an Outlook.com consumer mailbox is 50 GB. Exceeding this limit will prevent you from sending or receiving new emails.
Why can't I just set a different Exchange account as primary without removing them?
Outlook determines the primary Exchange account based exclusively on the order it was added to the mail profile. The first Exchange account added becomes the primary data file, so you must remove all Exchange accounts and add the desired primary account first.
What does 'Compact Now' actually do in Outlook?
The 'Compact Now' feature reclaims empty space in your Outlook data file. When you delete messages or attachments, the file size doesn't automatically shrink; compacting removes this empty space, reducing the overall file size on your hard drive.
