I realize that we should be using an edge server and in time we will. However, we are just basically using lync 2013 on a single server for messaging only. Not interested in any audio visual yet. This has been working for months now just fine, however the server took a unplanned power outage and was shut down unexpectedly. After getting everything back up and running, I can only get lync working internally but not externally with messaging. Given me a DNS issue.
As a note, my exchange server was affected as well, but ended up I need to set the binding back for the SSL to the port that fixed that. No such luck with Lync. I am positive the topology is correct as it is working internally and even double checked everything. I checked the AD DNS for the SRV record and it works. I know it is something simple, but no idea what to look for at this point.