I had a case where a roaming user was connected to a public WiFi and got a certificate warning. The user saw the error and called me before connecting. Turns out the WiFi was doing SSL inspection. I was able to talk the user through the issue, and nothing was compromised.

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However, it is easy enough for the user to click Yes and bypass the warning. I am concerned a less-savvy user will ignore the prompt, leading to a security breach.

Is there a way to block Outlook (and other Office clients like OneDrive for Business) from connecting if there is a certificate issue? I looked in Group Policy but did not find anything. Maybe I am missing it.

Note we are using Office 365 for e-mail, but I think this would apply to on-prem Exchange as well.

  • See also So Long, And No Thanks for the Externalities: The Rational Rejection of Security Advice by Users. "We argue that users' rejection of the security advice they receive is entirely rational from an economic perspective. The advice offers to shield them from the direct costs of attacks, but burdens them with far greater indirect costs in the form of effort. Looking at various examples of security advice we find that the advice is complex and growing, but the benefit is largely speculative or moot."
    – sebix
    Oct 12, 2015 at 18:44


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