I use Internet-ID connection. All works well when for most of deployed computers but there are cases that deployed computers can send e-mails to me, but I cannot logon. I have no control on user network configuration. All computers are tested on my network and are connecting fine. Any comments? May be using direct connection would be better choice since I have no control on client site. Is this port issue. How can I debug?
Direct connection is always a better choice because no mediation occurs and (in theory) the perceived speed and responsiveness should be better.
However, the Internet ID connection should work anyway except only rare occasions where the network environment on the Host side is extremely strict. Please, note that even with the Internet ID connection the Host should be able to communicate with our mediation servers on the Internet, that is - establish an outgoing connection at certain port. Oftentimes, especially in corporate environments, all outgoing ports are blocked except those used commonly, such as port 80 and 443.
I'm more than sure that if you set up your own mediation server, set it up to use port 443 and then point the Host in question at that mediation server and port - everything will work.
I might be mistaken however in that it's a port issue and not something else, in which case it's recommended to check this Knowledge Base article that might help to troubleshoot the issue.