It's been causing some major confusion recently, did you know that Steam now blocks most major email address' in their chat program?
After talking to a friend of mine and asking for his email, I received a message from him saying "http://gmail.com." At first I thought he was trying to troll me so I went along with it, later on after some more frustration we realized that Steam chat was actually blocking what we were sending to each other.
As you can see above, on the left I sent him a few different test emails to check exactly what is blocked. His result is on the right, showing that all of these email address' have been effectively turned into URL's. For those who don't keep up with Steam updates and patch notes, this little bit of news may cause you some headaches in the future.