Question:
When changing users from Cached Mode to Online Mode in Outlook and deleting the OST file, after starting Outlook the OST was recreated and continued to grow.
Recreating the problem:
New Profile created in Cached Mode and OST is created
You uncheck Cached Mode option in Outlook
Close Outlook and manually delete the OST
You launch Outlook again and shows in Online mode
But when you look the OST file was recreated and starts to grow in size
The Solution:
The problem we were running into here was due to a GPO setting was enabling folders for offline use, and by just unchecking Cached Exchange Mode that did not remove the Offline Use settings on the folders so the OST would still get created
Here is the GPO that was effecting this environment, it was set to "Download Headers and then Full Items" which is fine and what they want it just means we need to get an extra step when moving users to Online Mode and not wanting the OST to be recreated
After changing an profile from Cached Mode to Online mode if you check your Send/Receive Group settings you will notice that folders are marked for Offline Use still.
Tools, Send/Receive, Send/Receive Settings, Define Send/Receive Groups
Under Folder Options some default folders are selected.
To fix this and stop it from recreating the OST file
Close Outlook
Go to Control Panel and Mail
Select the profile you are working with, go into the profile properties and More Settings, and select the Advanced Tab
Select Offline Folder File Settings
Select Disable Offline Use
Select Yes
Close out of the Profile settings and manually delete the OST file again
ReOpen Outlook
You will notice that the OST does not get recreated now and in your Send/Receive groups your folders are not marked for offline use:
Note, this was the solution for this environment, it might be different in others.