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Blair Benjamin
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Intermittently cannot open Outlook - "The set of folders cannot be opened. Network problems are preventing connection to Microsoft Exchange."

Having intermittent issues opening Outlook 2016 and having it behave properly.   I will often get the following message when trying to open it - "Cannot start Microsoft Outlook. Cannot open the Outlook window.  The set of folders cannot be opened. Network problems are preventing connection to Microsoft Exchange."

Sometimes if I leave it closed for a little while, it will eventually then open again.   However, other mailboxes which I have full access permissions to  will not expand properly and kick back that similar message again.  Specifically, "Cannot expand the folder.  The set of folders cannot be opened...".  As an admin, I have full access permissions to various mailboxes, but most of them aren't expanding right now.  

Just to offer more background info, over the past several months we have been migrating from Exchange 2010 to 2016.   They are both still currently running, but most everything is routing to/through the new server.  Just have a few more mailboxes to migrate from 2010.   The specific mailbox in question here that is having issues is on 2016 and the client is running Outlook 2016.  It had been working OK, up until a couple weeks ago, well after having been migrated to the 2016 server.  I can't trace the origin of this issue back to a specific event, transition, migration, or whatever.

I do suspect that the issue is somehow more on the server side than the client side.  On the client side I have deleted the mailbox profile, run a repair on Office/outlook, restarted the computer, you name it...

Not sure what else to try or look for.  

Thanks in advance for any ideas or suggestions.

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Jitendra Kushawaha

8/22/2022 - Mon

Are you using any PSTs or are all the accounts OST based?  PSTs frequently cause that error if they are large or on slow hardware/connecting through a slow link.

I used to use OffCAT but it has been replaced by the tool below so you might give that a try:


Hope that helps!
Robert Retzer

Try to recreate the user's outlook account, all there ost come from the server anyway so if you delete the user's outlook profile and recreate it it should automatically grab the ost file from the server.  How large is the user's profile shown on the exchange server? If the file is large the file on the computer may be corrupted and recreating the user profile may resolve the issue. If the file is large note it may take some time before all the folders and their contents to populate after the rebuilding of the account.
Edwin Hoffer


If your Outlook account is configured in POP account, it will be creating PST files. In such case you can refer the link given below:


Otherwise in case of IMAP, Exchange configuration, OST file will be created at default location. In such cases, as the above expert suggested, you can deleted the existing .ost file from your system. And now your MS Outlook account again. It automatically creates a new .ost files for your account.

Hope this may help you.

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Blair Benjamin

Thank you all for the contributions thus far.   Here's what I can say in follow-up...

1- It's .OST based.  No .PST files.  I'm connecting to Exchange.
2- I downloaded and ran the SaRA tool.  It did not identify any problems.
3- I have deleted the Outlook profiles and data files on several occasions and re-created them.  Sometimes it seems to help, but I think it's just a by-product of the next point.

When I close out of Outlook and try to go right back in a short time later, these symptoms persist.  If I stay out of Outlook for a good while and then try later, it seems to let me in.  Both yesterday and today, when I I started Outlook in the morning, it was behaving properly - including the folders for the other users' mailboxes that I have full-access permissions for.  However, if I close and re-open, we're back to getting the error messages preventing me from re-opening Outlook or, if it does open, being unable to open folders for those other users' mailboxes.

So, it seems to me that perhaps either Outlook or Exchange are not closing out connections properly subsequent to exiting Outlook.  I'm not entirely sure what it should be doing or isn't doing, but the fact that time itself seems to temporarily resolve issues/symptoms, that it must be something along those lines, but I'm stuck with making a meaningful determination beyond that. ??

Are all the "other users" mailboxes that you have access to on the new 2016 server?  If not I would migrate them over and then retest Outlook functionality.
Blair Benjamin


That's an interesting theory.  Several of the mailboxes I had full access permissions for were in fact on the old server.  I'm going to test your theory and report back.   It seems plausible that something like that could be coming into play here.
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Blair Benjamin

So, I went through and unlinked my account from full access permissions to any of the mailboxes that were/are on the old 2010 Exchange server and things seemed OK for a bit, but unfortunately it seems to just be consistent with the semi intermittent nature of this issue.  It is in fact persisting.  As I write this, I currently cannot open Outlook at all.  I'll probably be able to if I wait some time - perhaps an hour or two - but I'm definitely still having the issue.  I like the theory that was proposed, but no luck.  I fully realize that this is a difficult issue to troubleshoot and resolve from afar, especially since it's intermittent.  But I'm doing my best to provide full, accurate info and try common-sense things.   So, still open to other suggestions if anyone has any...

So disable cached mode in Outlook on your email account and report the results.  (run it in online mode)

Also, are you running any email protection on your workstation?  You might disable the email protection on your endpoint protection as a possible troubleshooting step.
Blair Benjamin

Already not using Cached Exchange Mode.  Not running any email protection programs.  Just have Windows Defender running, which is pretty normal/standard.
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James Murphy

Do you happen to be using a laptop or workstation that has wireless and a wired connection that are connected simultaneously?  Try disabling the wireless if that is the case.

Do you experience the issue while running Outlook in safe mode? (outlook.exe /safe)

I would use the "easy fix tool" in the article below to completely remove Outlook 2016 from your computer and then reinstall and test.


Past that you could try removing Outlook with Revo Uninstaller Pro and use the advanced option to clean out any orphaned settings that might persist through a regular uninstall.

P.S. Have you tried setting up the email account in Outlook 2016 on another workstation with success?  Just want to make sure that we are dealing with a local Outlook issue and not a mailbox issue.
Blair Benjamin

These are good suggestions and I'll try them.  However, the support.office.com URL does not work.

Strange...I clicked the link in comment and it opens fine for me.  I copied and pasted to another browser as well.

Here is another link that is at the top of the tree...(The sub item you want is the "Uninstall Office from a PC")


Hope that works!
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Blair Benjamin

That link is in fact working for me now. Must have been a temporary outage.  But thanks for that.  

I've done some additional troubleshooting.  I put a fresh/new install of Office 2016 on a totally different computer and I'm getting the same symptom.   Seems clear at this point that it's something server-side with this one particular account.  I think I'm going to next try just removing all other mailboxes that this account has full-access permissions for to see if one or more of them could be a contributing factor.   Definitely seems to be something server-side though, so if any other possible suggestions or ideas come to mind, I'm still accepting them.  :-)
Blair Benjamin

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Glad to hear you got it resolved and thanks for posting the solution you found as it will hopefully help the EE community in the future.
Jitendra Kushawaha

I had this issue with one of my client and when I installed below update... issue got resolved...


Your help has saved me hundreds of hours of internet surfing.