Sep 292017

There is a new issue starting to be visible in the last couple days that I’ve noticed across 3 fully patched systems (Windows 10 running Outlook 2016 connecting to Exchange 2013).

When using Microsoft Outlook 2016 with Microsoft Exchange 2013, a password prompt becomes visible when opening an attachment in an e-mail. The attachment will open, however the prompt occurs after it’s opened, and only appears if an attachment is opened in the first place. The prompt will not appear if an attachment is never opened or highlighted (selected).

Outlook Password Prompt

When entering AD credentials, the prompt keeps re-appearing. When you hit cancel, Outlook will continue to function. You may also see the prompt shown below.

Exchange Password Prompt

After troubleshooting, I can confirm this is NOT related to any of the traditional “Outlook password prompt” issues that users normally experience due to misconfiguration, and I have a feeling this is related to either an Outlook 2016 update, or an update for Microsoft Windows 10 (and/or Microsoft Windows 7).

I’ve only found one other mention of this occurring on the internet which appeared a day ago, where multiple users are experience the same issue with Microsoft Office 365 with Microsoft Outlook 2016 with multiple operating systems (Windows 10 and Windows 7).

Microsoft Office Version: 1708 (Build 8431.2079)

As of right now I have no information on a fix, but I wanted to post this before other admins start ripping apart their Exchange servers trying to resolve this.


Update October 2nd, 2017: I’ve read that someone used the downgrade guide from Microsoft and downgraded their Outlook 2016 client to an earlier “Click-to-Run” 2016 version. This stopped the password prompt so it appears this issue has to do with the latest updates for Microsoft Office (Office 2016 and Office 365).

  21 Responses to “Outlook prompting for credentials (username and password) after opening attachment (September / October 2017)”

  1. Same issue here…so it’s not just you. For me it occurred after Exchange CU7 and Windows updates on the clients…

  2. Glad to hear it’s not just me!

    In my case, I think it happened either after Windows Updates on the workstation, or an Office 2016 update.

  3. Same issue here with Exchange 2016…

  4. Same issue here: Outlook 2016 last upate
    exchange 2016 cu17

  5. I have the same issue with Outlook 2016 (last update) and Exchange 2010

  6. I’ll take credit for that post about downgrading 🙂

  7. The issue is the new build. If you roll back the build it will stop. You will notice that outlook is creating a Windows Credentials for This is why it is not accepting the mailbox password because it is actually prompting for the microsoft password. If you use the microsoft password it will accept it. However, when you restart outlook it will prompt again. Its clearly a bug in the new build

  8. Same issue as well. I called Microsoft, Opened up a case, and they have had me do certain things to our Exchange server, which apparently has had nothing to do with it. I realized that other folks were experiencing it with the update of office, they just were not saying anything.

  9. Hi Daniel,

    Be really careful with what they suggest, and write down everything they ask you to change so you can change it back.

    Traditionally, password prompts with Outlook usually mean authentication issues, usually with the virtual directory config, IIS, AD requests, reverse proxies, UPNs, etc… All extremely common problems and part of the IT job managing Exchange, however this issue isn’t related to any of that (as I’m sure you already know, just writing this for other readers).

    Don’t want to be playing with those settings as it can be a pain to fix! 🙂


  10. Fix it by adding to local hosts file. But this works only because we have our on Exchange Servers

  11. Hi Rainer,

    I’m not quite sure if I’d be comfortable recommending that course of action. Doing this manually would be time consuming in large environments, I’m also wondering what types of other issues it could cause (delays, functions not working, etc…) since the Outlook client will start having timeouts when trying to connect (to whatever) to the local host.

    It’s difficult to say what effect this will have especially for other businesses that might have other software integrated with Outlook.

    I’m still recommending that most businesses just wait and deal with the prompts until Microsoft releases a patch.


  12. Same here. Outlook 2016 and on premise exchange 2016. Looks to be only affecting our microsoft surface users at this point but not 100% sure.

  13. Mike, interesting you say that…

    I’m using a Lenoxo X1 (with all the touch screen stuff enabled on Windows 10). I’m wondering if this might have something to do with that.

    Can anyone else confirm if they are having this same issue, and have the Windows 10 touch stuff turned on?


  14. Any updates on this issue? We have several machines having the problem

  15. Unfortunately no updates as of yet…

    I noticed on some other posts, someone mentioned that Microsoft is aware of the issue and working on a fix. I’ve noticed a few updates come across the line, but the issue is still occurring even running the latest updates.

    I’ll be posting an update whenever I get one! I’m actively watching this…


  16. Hi Stephen,

    We have a similar problem. We are on a hybrid exchange (Exchange 2016 On-prem and O365). This issues is only happening with the on-prem mailboxes (not all) with a O365 Proplus license. We have standalone 2016 MS Office license whihc works well. We engaged with MS Support and there is no fruitful solution till date. Really frustrated to have this issue un-resolved.



  17. Hi Sameer,

    Did this issue start recently with the update? I’m thinking that your issue may be one of the traditional password prompts related to IIS, Authentication, and Exchange.

    Please take a look at this article I wrote that focuses on UPN configuration, it might actually help your situation out:


  18. Reverting back to August 2017 Build 1707 Fixes the issue in the short term.

    For office 2016:
    Open an ADMIN command prompt and go here;
    cd %programfiles%\Common Files\Microsoft Shared\ClickToRun

    Then Type:
    officec2rclient.exe /update user updatetoversion=16.0.8326.2096

  19. Hi all,

    We use on-premise exchange server 2016 and users have outlook 2016. Since the last update in o365 we also had this problem. After searched for a lot, we finally found a “temporary” solution. By disabling the account lockout setting in the GPO settings we will not get the pw popups anymore. It’s not the safest way, but it’s best until a bug fix is ​​available.

  20. Hi WMM,

    Thanks for chiming in. Just curious, what was the specific setting you’re referring to? If you can, please try to go in to a little more detail as I’m sure your fix will help others (since it’s GPO I’m sure others will use it as it’s the most elegant fix).


  21. We’ve been seeing this a lot since September in our environment. Exchange 2013, no config changes at the time of symptoms starting.

    What I’ve found is that the credential prompt appears to happen when Skype for Business loses connectivity when Outlook is also open, either due to the network adapter going into a power-saving state, or the machine coming out of sleep. I can never reproduce the prompts with only Outlook being open and taking SfB out of the picture. So it seems that it’s the SfB/Outlook integration going wonky, SfB reconnects, and Outlook stays stuck at a credential prompt unless you reopen the client. Because of the sequence of events, Outlook looks like the sole source of problems when I do not think this is the case.

    Now why it suddenly started for so many people last month… no idea. We currently have a Microsoft Premier case open. I can reproduce this by putting Win7 and Win10 1703/1709 VMs into a save state and bring them back, or killing network temporarily. So I do not believe this is a hardware issue between this and the fact that with 3000+ clients, we never had complaints before September.

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