Our main IT person installed Lync on a Hyper-V instance, entirely standalone and away from our domain controller and Exchange server (which is also virtualized). Inside the building, within the domain, it works just fine; however when we attempt to log in to Lync from outside on computers and mobile phones not joined to the domain, we receive an error: "Can't sign in to Lync: There was a problem verifying the certificate from the server."
Our IT person claims this is because we need to install some certificates on these outside machines, as the computers joined to the domain get the trusted root certificate from the domain controller. I am thinking this is unnecessary, however could not find anything online regarding this requirement, which leaves me to believe that he set up the certificates incorrectly.
Are my doubts founded or unfounded, and is this indeed a requirement for machines outside the domain that need to access Lync?
Guidance would be appreciated. Thank you.