When Outlook redirects an Autodiscover operation from HTTP to HTTPS, you may receive a warning message that resembles the following:
Allow this website to configure email@example.com server settings?
Your account was redirected to this website for settings.
You should only allow settings from sources you know and trust.
Often, this happens if the DNS SRV record for the domain does not specify the correct TCP port to be used or if another Autodiscover response is received before Outlook checks the domain's public SRV record.
BEST PRACTICE: Mailprotector does not recommend suppressing this warning as it can be a good indicator of Autodiscover configuration problems. However, some circumstances with a client's environment may dictate that a root domain request for Autodiscover will always occur and the option to suppress the warnings is the workaround.
Autodiscover, Outlook 2016, Outlook 2013, Outlook 2010
Microsoft Support Reference
Detailed information is available on Microsoft's Support website.
Setting up a new Outlook Profile or account using Autodiscover may result in Outlook hanging or freezing. This can happen when the root domain responds to the Autodiscover request when port 443 (HTTPS) is closed.