Hi,
As the growth of the data file(.ost), the performance of Outlook may be affected.
We can compact the data file to reduce the size of the data file, check if this helps:
In Outlook 2013, click FILE -> Account Settings -> Account Settings -> Double click on the account name -> Advanced tab -> Outlook Data File Settings -> click Compact Now and OK.
(Note Depending on the size of the data file, it may take some time to compact the data file)
When the data file is damaged, we may face some unexpected issues in Outlook, running
Scanpst.exe should resolve the most of such issues.
For other users who need to keep all emails cached, I suggest they configure an AutoArchive to store some emails in a local .pst file and reduce the mailbox size:
How to Turn On the AutoArchive Feature
1. Click the File tab, and then click the Options tab on the
File menu.
2. Click the Advanced tab.
3. Click AutoArchive Settings.
4. Click to select the AutoArchive Every check box, and then type a number in the
Days box to specify how frequently the AutoArchive process runs.
5. If you want to be notified before the items are archived, click to select the
Prompt Before AutoArchive check box.
6. In the Default archive file box, type a file name for the archived items to be transferred to, or click
Browse to select from a list.
7. Click OK two times.
For more information about AutoArchive feature in Outlook, please refer to this kb below:
http://support.microsoft.com/en-us/kb/830119
Regards,
Melon Chen
TechNet Community Su