Got a user who travels back and forth from two locations (192.168.2.X and 192.168.3.X) and works remotely on two subnets and a basic windows PTPP VPN when on the road. Uses Outlook 2007 with Exchange 2007.
The exchange server is at a Data Center on the subnet there (192.168.1.X), so he is using Outlook Anywhere (outlook over HTTP)
At one of these locations (192.168.2.X), messages randomly stick in the outbox, and the user closes and re-opens outlook, and the messages send. This doesn't happen when they are at the other location, or using the VPN connection on the road. Doesn't happen in OWA as well.
There are about 20 other users at this location, and there are no reports of anyone else having this issue at this location, or the other.