We have been advised to do the following whenever we re-setup a profile in Outlook for our users. However we believe in performing non-destructive troubleshooting where possible. Is there any reason to perform the following steps.

  1. Remove any old Outlook Profiles
  2. Delete files with these extensions from the "AppData\Local\Microsoft\Outlook\" folder
    • .obi, .ost, .xml

I would say generally not. Recent version of Outlook do a fairly good job, in my experience, of not using files associated with another MAPI profile and there's virtually no "bleed through" of settings between disparate MAPI profiles.

If you're concerned about interaction with existing MAPI profiles and Outlook data files you could opt to rename the registry key (HLCU\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles) and directory containing the files (the AppData folder you mentioned in your question) while you're troubleshooting.


Blowing away a large OST file (particularly in today's world of hosted Exchange where it might take hours or days to re-cache a large mailbox) seems like something that shouldn't be done lightly. Keep that in mind when you start nuking files in the Outlook AppData folder. Even with an the mailbox server on the LAN you might have a multi-gigabyte mailbox to re-cache when the problem could have been solved w/o deleting the OST file and creating the network traffic and resource utilization in the server infrastructure.

  • Thank you for that. Could you think of any reason why it may need to be done? – Lee Carruth Dec 5 '11 at 17:30
  • I concur with Evan. I've created hundreds of Outlook profiles and I've never had any bleed through. I think I have 20 Outlook profiles on my work machine at the moment, from disparate Exchange servers, and have had no issues with it. – Driftpeasant Dec 5 '11 at 17:31
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    In my opinion there's no harm in not doing it and there's no harm in doing it. Whomever instructed you to do it probably did so because they like to start with a clean directory structure, with no detritus from any previous profiles left hanging around. I must admit that I'm a bit of a neat freak and would probably do it, if I had occassion to create new Outlook profiles on a regular basis. – joeqwerty Dec 5 '11 at 19:13
  • I agree with Evan that its perfectly possible & with joe that it doesn't matter much either way, so I would ask, Lee, why do you want to keep the files (.OST file aside)? I can't see you losing data from deleting them and if nothing else, if detritus like this never gets cleared up then it all adds cost to the time & expense of backups and file server management, etc. – Rob Moir Dec 5 '11 at 19:35
  • Another reason to "keep things tidy" is to ensure a consistent environment, which helps for tech support purposes. I don't fancy walking a user through deleting that one file from a folder containing the remains of 20 MAPI profiles that all generated a bunch of files with similar names! – Rob Moir Dec 5 '11 at 19:40

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