Outlook takes several minutes to connect to Exchange Online (O365)

In the last few weeks, I have come across a few companies which are having slow Outlook connection issues to Exchange Online. There are many reasons why this could occur, but I want to focus on one of them for now. This is a scenario where after opening Outlook 2010 / 2013, it takes about 2 minutes to connect to a mailbox.

If Outlook is going via a proxy server to Office 365, there is a specific issue which occurs if you have manually configured your proxy server address in IE (see screen shot below as an example). That is, Outlook thinks some IP ranges in Office 365 are internal, and therefore doesn't route the requests via the proxy server. Specifically, if you do a network monitor trace, you will see requests to a 132 and 154 range, are not routed to the proxy server.



How to solve this, some options:

  1. Microsoft recommends that Outlook doesn't go via a proxy server when connecting to Office 365, instead it should have direct access to the internet (Office 365). There are many reasons why it is recommended to bypass proxy server e.g. performance.
  2. Unselect “bypass proxy server for local addresses” in IE manual proxy configuration screen. This is a quick one to test, to see if you are a victim of the issue.
  3. Have IE automatically detect proxy settings instead of manual settings (there is a larger discussion to be had on how this works than we have time for here)
  4. I haven't tested, but perhaps a PAC file will work to force the connection to the proxy for those IP ranges.


Note: this looks like it might be a bug, but not confirmed yet. Therefore, this issue could be resolved in a future update to Outlook. For now, you will need to go with one of the recommended fixes above. Or, post an alternate suggestion to help the community out.

Update: this was confirmed to be a bug, and Microsoft has released a hotfix and process to resolve it. This is described here: http://support.microsoft.com/kb/2916915. Personal opinion is that I still prefer the auto detect option with proxy pac file though as a solution.

Comments (13)
  1. Dyanne Rossi says:

    FYI, have been in discussions with Microsoft on this today.  Extract from results of our case :

    The behavior is considered by design and it is addressed in Critical Design Change Request.

    We have scheduled a fix for Outlook 2010 in February 2014 cumulative update. A fix for Outlook 2013 will also follow, but Outlook 2007 will not be addressed because it is in Extended Support.

    There are two possible workarounds for this behavior:

    • First, and I wouldn’t recommend it, is to allow Direct traffic through the Firewall to Office 365.

    The advantage of this approach is that it will be done centralized and it will impact everyone immediately.

    Information about the O365 IP addresses onlinehelp.microsoft.com/…/hh373144.aspx

    There are two downsides to this behavior:

      o first you need to maintain the Firewall exceptions as IP from O365 server can change without notice

      o second, winhttp traffic may go through both proxy and direct and this can cause unforeseen behaviors.

    • The second approach is to use a proxy pac instead of manually setting in the proxy and the exceptions.

    The advantage is that you will have centralized method to control how winhttp traffic goes and the issue will not be experienced anymore.  However, you may have some challenges with deployment and connectivity topology so a single pac might not be fit.  Yet you can configure proxy pac files for each site requirements and use an IIS server to store it.

  2. Thanks for giving feedback on this Dyanne, much appreciated.

  3. Mike Giles says:

    Thanks for posting this issue, I've been struggling with this for quite some time now.

    I'm seeing the delay with Outlook 2010 Anywhere on a Windows 8.1 machine (all fully patched) when connecting to Exchange 2007 servers too.  When the 'Bypass' box is ticked, it takes between 2-3 minutes for the login prompt to appear.

    The way I spotted it, was by dropping to a cmd prompt during the delay and running a netstat -a which shows a connection attempt being made directly to an IP address rather than the proxy address.  Once the IP address connection fails, it then makes use of the proxy configuration as it's supposed to.

    As a secondary issue, the use of a proxy pac file has limited success too.  Elements of Outlook 2010 Anywhere use winhttp to make a connection to the servers but winhttp can't use proxy pac files (that have been entered into the 'Use automatic configuration script' field above) so this connection completely fails 🙁

    Looking forward to seeing the fix coming out !

  4. Paul-Smith says:

    Excellent article, thanks!

    Its early days but a quick test this morning shows the issue is still present with Office 2013 SP1.

  5. Ricardo Utreras says:

    Many thanks!

    This workarround solved the problem to our Outlook 2010 and Outlook 2013 clients using explicit proxy in their browsers..

    ¿There be a a fix to this someday?

  6. Jay says:

    This is the following fix for the Outlook proxy workaround


  7. Jesper Ståhle says:

    Fix for Outlook 2013: support.microsoft.com/…/2878323

  8. Andi says:

    Hotfix works for me on Windows 8.1 with Office 2013, Win 7 with Office 2010 does not work after fix.

  9. Here is a KB article which describes the fix process support.microsoft.com/…/2916915

  10. MT says:

    As per the infromation above for an outlook 2010 SP2 client I had to install the below hotfixes



    I also had to create the below registry Key

    HKEY_CURRENT_USERSoftwareMicrosoftOffice14.0OutlookRPCEnableForceHttpProxy value 1

    However this is only good from computers on premesis, as soon as a laptop user goes offline they are forced to use a proxy which they cannot, this result in ZERO connection so for most of our user base this has just shifted the problem.

    I am trying to figure out what we can do to fix this 4:20 connection issue for all users no matter how they connect.

  11. runiuksp says:

    We've the same problem with proxy and with users accessing Outlook from home.

    Enabling this causes no connectivity to Exchange:

    HKEY_CURRENT_USERSoftwareMicrosoftOffice14.0OutlookRPCEnableForceHttpProxy value 1

    @MT – did you find any fix for this?


  12. andyk1029 says:

    Same problem here too with proxy and accessing outlook away from office.

    MT , Runiuksp did you ever find a fix for this?

  13. Jean-Pierre says:

    Dear Microsoft, I am paying you every year for our Action Pack and also for some accounts on your Office365 platform.

    However, connecting to your servers is taking 1990's style delays. All my websites and other internet resources are OK, but going to Office 365 portal, or letting Outlook connect to the Office365 servers to fetch mail is taking unacceptable times, in terms of 30+ minutes!

    I am not sure if I can still take your services serious… and I hope for a good solution.

    It also doesnt make any sense to me that these forums mostly dont include any official response from your side Microsoft. I would fix that too, maybe just allocate a few of your ten thousands of employees to keep an eye on the questions asked.



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