Recently I checked my mailbox size in server that is 50 GB. Also, when I check the mailbox size in Outlook by right-click on Properties, it is 50 GB. But when I look at the size of items in list, it is around 4 MB. I also checked Outlook folders individually, but the size is not close to 50 GB. I am puzzled with this issue where my OST file size is not matching with mailbox size. Can anyone help me to reduce the mailbox size?
With this query, we have decided to resolve this issue through this post. We will talk about this issue in details and ways to resolve it.
OST file is exact copy of user’s mailbox. It’s size can’t reflect mailbox size. Apart from mailbox items, there are other items as well in the file that takes larger space. Items stored in OST file depends on whether you are using IMAP account or Exchange account.
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In case you are working with Outlook 2013 or higher edition, the size of OST file will be lesser than mailbox.
Why OST File size is larger than Mailbox?
Given is the list of items that are saved in OST file of Exchange Server account that results OST file size large than mailbox.
- Mailbox items like emails, notes, contacts, calendars, journals, tasks, etc.
- Public folders added as favorites
- Hidden items and other overheads found in PST file
- Shared folders of additional mailboxes
- In MS Outlook 2016, two connectivity modes are there when you connect to Exchange Server. These are Cached Exchange Mode and Online Mode.
With Cached Exchange Mode, Outlook does not depend on continuous internet connectivity to access the details. However, proper contacts to Exchange Server is needed to perform few tasks, even when configured in Cached Exchange Mode. These tasks working with shared folders are not available offline. Also, working with Outlook 2016, OST file is saved locally on the system, might be 50-80% larger than mailbox size. In Cached Mode, the format used by Outlook 2016 to save data locally is less-sufficient as compared to server data file format.
If your mailbox stores large number of files in single mailbox or the mailbox is too large then it results Outlook freezing or not responding. In this situation, users need to deal with large size OST file.
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Solutions
- Recreating OST file: For mailbox cleanup, users have option to let Outlook recreate OST file. With this, users get new OST as Outlook is started.
- Using Synchronization filters: Users can set synchronization filters if they have large folders. This synchronizes the items and saved in OST file as it caches only recently received items as per the filter.
- Apply Sync Slider: Sync slider is there which sync only recent emails of 1 month, 3 months, 6 months or 1 year instead of complete mailbox.
- Remove Public Folder Favorites: You can remove some public folder favorites to reduce the data volume that is being cached.
- Apply Archive Policy: Archiving helps users to clean mailbox and improve Outlook’s performance.
- Disable Shared Folder Favorites: You can choose option disable shares folder favorites. With this option, it will not cache the shared mail folders and helps in reducing OST file size.
Conclusion
Outlook is used by majority of users and it is important to resolve every issue of it to work properly. Through this post, we have discussed one such issue related to OST file size. You can try to fix it with discussed ways but if your OST file corrupt, then go for OST to PST Converter to recover & restore the data.