If for some reason there is a firewall or port blocking device between ServiceDesk and one or more of the supporting servers the following ports will need to be open between ServiceDesk and the server(s).
 

1. Communication  to SMP is on port 80 or 443 depending if using http or https
2. Communication to AD server is on port 389
3. Communication to mail server is port 25(smtp), and either 110(POP), 143(IMAP), 995(POP over SSL), or 993(IMAP over SSL) depending on what email protocol is being used and whether using default ports
4. SQL default port is 1433

If you use telnet to confirm that the above ports are open between ServiceDesk and the servers on the other side of the firewall then ServiceDesk will be able to communicate between servers.