I recently confirmed that transferring a file with the Communicator client across a firewall is not a supported feature in OCS 2007 R2. This surprised me, and I see many others in the OCS forums have struggled with firewall ports in an attempt to get this working. Equally surprisingly is that this does not seem to be officially documented anywhere. I have updated my popular “OCS File Transfers – Key Facts & Common Cures” post to cover this scenario.
Note: this will be supported in the upcoming release of OCS – Communications Server “14”.
The key requirement for a Communicator file transfer to work is that each client needs to be able to locate each other on the network. If a firewall exists on the network path between the client end-points, the file transfer will not work. File transfer scenarios such as one internal Communicator client (inside a corporate firewall) and one external Communicator client (outside the firewall with no VPN) are not supported.
Attempting to transfer a file in MOC without each client able to locate each other directly produces the dreaded “You cannot receive the file…. This may due to firewall restrictions or network problems” as shown below.