The popular Google GMail web-based email service now offers POP and SMTP services. With 1GB of free space, I am sure that a lot of students and faculty members have one. This is quite typical for a university setup - one gets the official university email and then have one or more free email accounts from third party companies with Yahoo! and Hotmail being two of the most popular.
Why am I talking about this here when this is already common knowledge? Well, here is the thing - the moment that GMail started to offer their POP via TLS/SSL services, which uses port 995, our users started to configure their Thunderbird, Outlook, Eudora or Mail.app clients to get their GMail messages. Unfortunately, due to security reasons, port 995 has been closed (thanks to worms, trojans and virus and to Microsoft, of course!). Naturally, users contacted our help desk asking for the reason why they couldn't connect.
What we did was to allow port 995 access ONLY to one server, which is Gmail's POP server. However, if someone spoofs Gmail's servers, we're in trouble. 🙂