To fix an OST file for an Exchange account, you simply delete it and let Outlook rebuild it from the server: For a non-Exchange account OST, such as IMAP, use the Scan PST method in the first section of this article. If the above steps did not help, please try renaming outcmd.dat, and as described in Part 2 of this article.Running unnecessary add-ins may make Outlook slower and even cause stability issues. You probably have more add-ins installed than you think.
Note: You can also use scan PST to check and fix your OST files. In addition to PST, OST and profiles, Outlook has several other files which might get corrupted.
If you are experiencing issues with your Outlook, try these items one-by-one and hopefully one of them will help.
By far the most common reason for Outlook crashes, instability and unexplained weird behavior is a corrupted PST or OST file.
These Outlook data files may be either personal folders (.pst) files or offline folder (.ost) files.
The expected behavior is as follows, dependimg on your or data file size.: So if you can, delete your unwanted mail to reduce size and ensure that auto-archiving of old Outlook items is enabled. Microsoft has provided Inbox Repair Tool as well as a Fix It, which lets you recover folders and items from corrupted Personal Folders or files.
While it is always a good idea to optimize & speed up Outlook from time to time, you may at some time face this issue.