Azure MFA with office phone extension - supported or not?

Question

Our users have had the option to use an office phone with extension to verify MFA for quite some time. Today I started receiving reports from users that they weren't getting calls when using office phone for their additional authentication. Now I'm seeing that Microsoft recently updated their documentation regarding Azure MFA and do not support extensions in phone numbers.

On mysignins.microsoft.com, office phone with extension is still listed, and the initial call after registration does go through to the extension, but any further calls after the registration call will fail with error code 500121. Has Microsoft removed support for Azure MFA authentication using office phones with extensions?

Answer 1

Thank you for asking this question on the Microsoft Q&A Platform.

Your research is correct, phone extensions are not supported.

Hope this helps!

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