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

  • Article

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.

 

image

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: https://support.microsoft.com/kb/2916915. Personal opinion is that I still prefer the auto detect option with proxy pac file though as a solution.