I have thousands of users connecting to my Lync servers, probably hundreds of them connecting via mobile devices. All of the desktop clients and almost all of the mobile clients are able to connect using autodiscover. Enter your username and password, Lync finds your server based on your domain name, and viola, you’re connected. Unfortunately, some iOS devices haven’t been cooperating lately. They return this error:

Cannot verify the certificate from the server

It sounds like a certificate problem, right? Well, maybe somewhere under the hood it is, but installing all the right certificates on the iPhone or iPad using the iPhone Configuration Utility per this Microsoft article didn’t help. Same error.

One of my coworkers, while perusing the MSDN forums, discovered that the Lync Mobility client doesn’t connect in the same way as other clients. (Or some Lync Mobility clients. I still can’t figure out why some iPads work with autodiscover and some don’t.) If you get this certificate error on an iOS device, don’t rely on autodiscover. Set the Auto-Detect Server option to OFF and enter this for the internal and external server addresses instead:

https://lyncserver.domain.com/autodiscover/autodiscoverservice.svc/root

Obviously, you’d replace “lyncserver.domain.com” with the name of your own Lync server.

This works on Lync 2010. I don’t know about Lync 2013.