When Microsoft 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? https://mail.cpandl.com/autodiscover/autodiscover.xml Your account was redirected to this website for settings. You should only allow settings from sources you know and trust.
When this warning message occurs, you may choose not to be asked about the specific website again.
You or administrators may want to suppress the initial warning message for a specific HTTP redirection that is expected in your organization. This article contains information about how to do this.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
To configure Outlook behavior when HTTP redirection occurs, you can set or deploy a registry value. To do this, follow these steps:
Start Registry Editor.
In Windows Vista, click Start, type regedit in the Start Search box, and then press ENTER.
If you are prompted for an administrator password or confirmation, type the password, or click Continue.
In Windows XP, click Start, click Run, type regedit in the Open box, and then click OK.
Locate and then click to select the following registry subkey:
Where xx is 14.0 for Outlook 2010, and 15.0 for Outlook 2013.
Click the Edit menu, point to New, and then click String Value.
Type the name of the HTTPS server to which AutoDiscover can be redirected without prompting for confirmation from the user, and then press ENTER. For example, to allow redirection to https://adatum.com, the first String Value (REG_SZ) name would be:
Note In Outlook 2010 the name of the server is case-sensitive. In Outlook 2013 it is not case sensitive.
There is no need to add text to the Value data box. The Data column should remain empty for the string values that you create.
To add additional HTTPS servers to which AutoDiscover can be redirected without displaying a warning, repeat steps 4 and 5 for each server.
On the File menu, click Exit to exit Registry Editor.
For more information about the Autodiscover service, visit the following Microsoft TechNet website: