The problem most likely lies with the proxy server. Since most educational establishments run proxy servers (to monitor, filter traffic etc) they will have tight access restrictions. I'm not sure exactly which software your school/college/university uses but with most proxy servers, you have to specify a list of ports in the access restrictions which can be used to send and receive traffic over. Most proxies will default to only have ports 80, 443 and 8080 in their configurations since they are the main ports required for web browsing. More ports can be added so that services such as MSN Messenger and mIRC can connect, and similarly ports will have to be unrestricted to allow MTA to be played. The trouble is, since the ports are defined at the hosts end, you won't know which ones specifically to be unrestricted, although I can tell you that the most commonly used ports are in the 22003-24000 range.
You may want to ask your network manager to look into this, just tell him/her what I've said above and I'm sure he/she will understand.