I've been curious about the safety of e-mail lately. As far as I know, the most vulnerable point of communication is the local network you send your mail from. That is unless you're trying to keep things from a government, which could use laws, lots of resources and possibly advanced SSL spoofing techniques. But snail mail is insecure as well.
That said, would it be safer to send sensitive data to an institution through snail mail or using HTTPS webmail? I realize that sending your data directly to the institution's HTTPS site is safer than both of these things, but lets restrict this question to snail mail and common HTTPS-enabled webmail services. The e-mail will have to travel over the internet; in other words it's not a Hotmail-to-Hotmail message.
I'm wondering specifically about how likely it is that your message will be intercepted and read by someone else.