We have an encoder machine that pushes content to WMS.  When these
machines are on our internal network the encoder had no issues pushing
to WMS.  However, when we plug the encoder into an external network,
we are no longer able to push.

We are pointing to the same machine/publishing point.  WMP has no
issues in reaching the publishing point to play content.

Is there some security setting that needs to be in place to make this
work?

The WMS is on our domain but the encoder is in a workgroup.

Thanks,
Mike