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Outlook losing connection to Exchange

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After adding the Exchange server to my Outlook, I'm getting many network connectivity errors to Exchange. It locks up Outlook for 20-30 seconds, including blocking other POP/SMTP sessions.

The visible symptom are messages something like "Outlook has lost connection to Exchange server and is attempting to reconnect" and then "Outlook has re-established connection to Exchange" popping up off the Outlook toolbar icon.  (Sorry, I don't have the precise wording now).

I'm running Outlook 2010 on Windows 7, and all patches and service packs are applied. My server is    I've been through all the "Test Email Configuration" recommendations that I've found online without fixing it... email configuration tests successfully and web interface to email has no delays. 

Any advice would be greatly appreciated.  This makes using Outlook extremely frustrating.

All Replies
  • Hi David,

    From your description,  I see there are some connection issues between your Outlook and Office 365 Exchange online . Please try the following steps for troubleshooting:
    1. Please re-run the desktop set up to see if any improvements. 
    2. If the issue still occurs, press Ctrl, and right click the Outlook icon on the system tray. Choose "Connection Status..." from the popup menu to see if the connection status is well. If the status are all established, please try to fix the issue by creating a new Outlook profile.

    Aaron Yuan
  • Hi David,

    How are things going now?
    I'd like to follow up this thread, do you need more assistant?

    Aaron Yuan 

  • Thank you for the advice.  Yes, I have re-run desktop setup on both computers.

    Yesterday I found a Hot Fix that seemed to address this (KB2598374) and applied it to both computers.  Note that both computers were previously Outlook 2007 and were upgraded to Outlook 2010 (and this KB mentioned that as a case)

    On one of the computers, the various changes over the last week have made the situation much better (not clear which one made the difference), on the other they have not.... it is still locking up for 30 seconds many times a day.

    Looking at Connection Status, the one that is working better shows numbers like this for the Request/Fail on each process:

    Directory  91 / 14

    Directory  125 / 18

    Mail   1921 / 10

    Mail   5311 / 18

    ... so over 99% of connection attempts are successful.

    The computer that is not working better shows numbers like these:

    Directory  553 / 331

    Directory  870 / 348

    Mail   4139 / 254

    Mail   3148 / 210

    ... so something like 8% of Mail attempts and 40% of Directory attempts are failing.

    I will try rebuilding the Outlook profile today on the computer that is not fixed and post the results.

  • Hi David,

    Thanks for your update.

    I know that you will try to rebuild the Outlook profile on the computer that is not fixed, if there is any update, please post here.


    Anna Shi

  • I rebuilt the Profile and that did  not fix the problem... still getting the same hig number of Failures.

    What to try next... is there any logging of the connections that I can turn on and see details of the errors?

    PS: I did check network connectivity of this computer with Ping and etc and there are no problems there.

  • Hi David,

    Based on current situation, I have some suggestions:
    1. Please check whether the time-zone is right on your laptop.
    2. Please refer to the following steps to check that whether Autodiscover works correctly.
    In a web browser, browse to
    On the Office 365 tab, under Microsoft Office Outlook Connectivity Tests, click Outlook Autodiscover, and then click Next.

    Aaron Yuan
  • Hello David,

    On the both pc's you mention, did you configure the same profile (mailbox), and do you have some other connected mailboxes in outlook?

  • Outlook Autodiscover ran successfully.... first two URLs failed then "HTTP Redirect" method succeeded.

    Time Zone is correct.

    Yes, both computers are connecting to the same Exchange mailbox.   That is the only Exchange they access; both also have another POP/SMTP account in their profile.

  • Hi David,

    In general, this kind of Outlook issue occur if your network environment is unstable or the network performance is slow, or the OST file size is too large and the Inbox folder or the Sent Items folder contains more than 20,000 items. Based on my experience, if these folder items or the OST files is large, the performance of Outlook can be affected. 

    In addition, please test with different location to check if it's a network connectivity issue.

    Aaorn Yuan
  • Hello David,

    There's some tweak you can try in outlook, but I didn't check it out yet myself  :

    It's not really a best practice I guess, but you might want to take a look, and see if it helps.

  • Thank you all, but...

    1)  This OST has exactly 2 emails, not 20,000.  The only reason we are using this connection is to share a calendar and contacts among multiple devices.. about 800 contacts and 2,000 calendar events.  

    Yes, the PST used by the POP account is very large... over 10,000 Sent Items and Inbox. But that shouldn't (?) matter to this Exchange connection

    2)  Everything feels good about the network connection... 54Mb wifi connection to the router 20 feet away, 6Mb cable internet, both with good ping times, no dropped packets, and good download speeds.

    I tweaked some settings in the Send/Receive groups, to try to separate the Exchange connection from the POP/SMTP connection, to hopefully cause it to not activate the Exchange connection when doing minor actions on non-Exchange emails (simply closing an open POP email window would cause Exchange to try to connect and completely lock up Outlook for 30 seconds).   I don't know if that will make any difference.

    I see that many other people have raised exactly this same issue here in the forums, with many different situations: small home networks like mine, large businesses with 1000+ users, etc. etc.  And none has reported any definitive solution to the problem.  Is this perhaps something that is just not well understood?

  • Hi David,

    I understand that Outlook 2010 cannot be connected to Exchange Online properly. In this situation, I suggest you perform the following steps to narrow down the issue.

    Step 1: Enable Cached Exchange Mode
    1. Click the File tab, click Account Settings , and then click Account Settings .
    2. On the E-mail tab, select the user’s Exchange Server account, click Change , and then make sure that the Use Cached Exchange Mode check box is selected.

    Step 2: If the problem continues, try restarting Outlook in safe mode by running the following command from the Run box or from the Start Search box on the Start menu:
    outlook.exe /safe

    Step 3: Repair Outlook
    1.  In Control Panel, open the Programs and Features or Add/Remove Programs window, and then select your version of Office from the list of programs. 
    2.  Click Change . 
    3.  Click Repair, and then click Continue. 

    Step 4: Test the issue in Clean Boot Mode, refer to

    Please post the results here for further research.

    Mindy Pan


  • Just to let you know that I do have the same problem and I'm becoming really desperated of not finding any good answer to solve it..


    This is a weird issue because if I setup one of the accounts in another network it works really nice. If I setup the account in my network I do always have the outlook disconnecting and reconnecting.. I contacted my ISP and gave him a packet capture. He told me that on his side, everything is OK. I disableds my A-V, changed the MTU, disabled a lot of security in my router, setupped the account on different computer and I still have the problem..

  • Hi Informatique Inpro,

    I understand that Outlook can work properly in another network environment. I suggest you test the Outlook connectivity issue in Clean Boot Mode. If the issue persists, please create a new thread on the forum with detailed information such as screenshots. This is so your question will be answered quickly.

    Mindy Pan


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  • Hi David,

    Do you have any updates about the Outlook connection issue?

    Mindy Pan