I think this has nothing to do with Chrome and is a feature of Windows. What happens when you select the default mail? Do you get the same prompt the next time you try to do it?

Once, the user did select Outlook as the default mail, the problem is no more existing on this computer. That problem was see by more than one people in my L3 team.

Did you test what I explained in the case?

I'm sorry you're having issues with this. This doesn't seem like a problem with Chrome, but rather a feature of Windows. This is just how they decided to do it, I don't think anybody is gonna change it. And in the end, what's the big deal with having to choose the default option once, right? :-)

The issue is peoples will call the support center. It is a problem. How are you concluding it is a feature of Windows and not a Chrome problem?

Chrome is a valid email client (to support web-based email providers), and Windows prompts users to select what app they want to use to send emails, so this is indeed Windows behavior.

If this is causing support calls, you might want to use group policy to specify Outlook as the default email client: https://support.microsoft.com/en-us/help/2008044/how-to-configure-the-default-e-mail-client-using-group-policy

I disagree. Once the email client is set, why would Chrome installation would force the user to select an email client again? Once the choice is made, Chrome should not provoke that behavior.

I think we could see this as a FR for a new master pref/policy for Chrome not to register as a mail handler. WDYT?

I agree. Usually, how long does it takes before fixing it? How do I know when there are new pref/Policy?

Re: master prefs - I thought we agreed not to add new functionality to master prefs but to use policy everywhere for new feature requests?

Has it been sorted out already? I'm experiencing the same situation with the latest W10 1803 and Chrome browser - after fresh build there is default MAILTO: protocol set up to Outlook 2010 -> after Chrome installation, selection box was cleaned up and ther is "Choose a default" option available.
People from business are complaining about this, as the want to have still Outlook as default MAILTO protocol apps. Such Chrome behavior is unacceptable! 

Reopening, assigning to privard to triage. Does sound like something we'd like to have a policy for (don't have Chrome register as a mail handler so users aren't asked to pick between possible mail handlers in windows UI).

Again, I think the real solution is for admins to actively select a mail client for their users (https://support.microsoft.com/en-us/help/2008044/how-to-configure-the-default-e-mail-client-using-group-policy), but for admins that don't want to (or can't) do this, but know that they don't want Chrome to be the mail client, this would be a secondary option.

After last test:

Chrome installed -> MAILTO cleaned up from Outlook 2010
Chrome uninstalled -> Outlook 2010 goes back
Firefox installed -> MAILTO still Outlook

Above test proves unacceptable Chrome behavior for business users. Why Chrome changes by default MAILTO defautl appliaction? We want keep it with Outlook 2010. Please clarify this issue.

Action with creation own GPO tepmplate (adm) does not make any sense - I did it and added to local policy (Computer Configuration -> Default e-mail client = Microsoft Outlook, status = enabled) - finally results are the same
and Chrome still change MAILTO protocol after installation.

Can you please let me know why Firefox does not do this, but Chrome does it?

Can I get any official statement from Google about above issue?
Issue is not sorted out, business users are complaining, so we are considering replacing Google Chrome with Firefox.

Hi. I don't believe it's the case that Chrome is stealing mailto handling from any other program -- Chrome has never done this, and Microsoft has made it nigh impossible for any program to steal a user's URL association in Windows 10. That said, I believe that Chrome does register itself as "capable" of handling mailto as per https://docs.microsoft.com/en-us/windows/desktop/shell/default-programs. If memory serves, this is so that Navigator.registerProtocolHandler (https://developer.mozilla.org/en-US/docs/Web/API/Navigator/registerProtocolHandler) functions as expected. If some web site (e.g., outlook, hotmail or gmail) wishes to be registered as the mailto: handler, then Chrome needs to be registered as the system mailto: handler so it can bring the user to their chosen mail site when they click on a mailto: link on the web.

So what changed in Windows 10? Among the many changes that Microsoft made in Windows 10 was the addition of a prompt to let users choose their default programs. I believe that this dialog appears for a given protocol after the user chooses any action to use that protocol following the installation of a new handler of it. This, to my understanding, is the primary way that a user can pick any non-Microsoft handler for a protocol. Using http: for an example, installation of any web browser (Firefox, Opera, Chrome, etc) will cause the next attempt to open an http: URL from Excel to ask the user to pick which web browser they wish to use to open it.

I will take a look at what Chrome is doing to confirm my understanding. While one may think "Chrome shouldn't register to handle a protocol until a site uses registerProtocolHandler to request it", I don't know that this is feasible since I seem to recall that registering to handle a protocol must be done at high integrity, whereas Chrome runs at medium integrity.

Anyway, we appreciate your feedback and understand your frustration. We'll take a look at our options. Off the top of my head, it seems that the new prompting policy in Windows 10 is what's leading to your frustration. The remedy there is to use Microsoft's prescribed techniques to make Outlook the mailto handler for all users in your organization via Group Policy.

BTW, I suggested exactly this (set Outlook as the mailto handler via GPO/Intune/etc) in comment #5. I'm not sure why that solution isn't acceptable though (maybe restrictions on setting GPO?)

BTW: the way to set a default protocol handler via GPO in Win10 requires creation of a "default associations configuration file". Microsoft explains how to use one to make IE11 the default browser here: https://docs.microsoft.com/en-us/internet-explorer/ie11-deploy-guide/set-the-default-browser-using-group-policy. The same technique can be used to set the "mailto:" protocol to Outlook.

I've taken another look at what's going on here, and it is indeed the case that Windows asks users "How do you want to open this?" where the first option is under a heading "Keep using this app". This is the Windows behavior when an app installs and advertises that it can handle the URL Protocol. So the questions we're left with are:

1) Is it okay for Chrome to *not* register for mailto (and the other protocols here: https://cs.chromium.org/chromium/src/chrome/installer/util/shell_util.cc?type=cs&q=kPotentialProtocolAssociations%5C%5B%5C%5D+file:shell_util%5C.cc&sq=package:chromium&g=0&l=1512)?
2) Should we introduce a knob that admins can use to suppress registration of mailto (and the other protocols)?

For #1, Chrome would need to pop UAC for sites that use registerProtocolHandler for mailto (or any protocol not in kPotentialProtocolAssociations). This is a very bad user experience, and would interfere with respecting the user's intent, especially in cases where users cannot UAC.

For #2, it seems to me that this would be adding complexity to Chrome to handle behavior in Windows that Microsoft has deemed provides the best user experience. This doesn't seem like the right tradeoff to me. As has been mentioned several times above, administrators who wish to enforce a particular URL protocol -> application association should do so via the existing policy controls for Microsoft Windows.

I'm closing this out as WontFix for now; we can continue the discussion if anyone has anything constructive to add. I am sensitive to the frustration that some admins/users are experiencing -- I think it would be better to bring the issue up with Microsoft, as Chrome is following MS's documented practices.