I have 3 computers in my network connected to the same router.
Computer A - my desktop computer Computer B - Web server Computer C - Mail server and SQL server
Everything is set up correctly externally which means I can telnet to IMAP port (143) on Computer C and Web server port (80) on Computer B.
But suddenly, in like a 10 minute interval or more often I cannot telnet to Computer C from the outside. I can telnet from Computer A and B. And I can telnet from Computer A to B from the outside.
I do not think the problem is the router. Computer C is new with Windows 2012 and I guess it is either a network problem, configuration etc on that computer. Do you have any more ideas of how to test this or?