Ideally, outgoing TCP connections to all ports (1..65535) should be opened. This option results in Skype working most reliably. This is only necessary for your Skype to be able to connect to the Skype network and will not make your network any less secure.
If the above is not possible, open up outgoing TCP connections to port 443. This will only work if you are using Skype version 0.97 or later.
If the above is not possible, open up outgoing TCP connections to port 80. Some firewalls restrict traffic to port 80 to HTTP protocol, and in this case Skype can not use it since Skype does not use HTTP. In some firewalls it is possible to open up all traffic to port 80, not just HTTP, and in this case Skype will work.
If the above is not possible, Skype versions 0.97 or later can use a HTTPS/SSL proxy. In order to do that, you have to configure the proxy address in Internet Explorer options. Then Skype will be able to use it as well.
Please let me know if this answer could help you solve this issue. If not, let me know asap in order to give you a better and deeper answer over this scenario.
BR,
Javier Koumian.
javier.koumian@fibertel.com.ar
