Recently I was trying to send the following text via Windows Live Messenger chat client for a business reason but he never received the message, and I wasn't informed that the message hadn't been sent successfully.
[Conchango.VSTS.Scrum.ReleaseNumber]
The reason was that the text included the letters .scr which is one of the tokens that the msn messenger servers filter out by simply dropping the message and not informing either user that the message wasn’t delivered successfully.
See the following links for more information on this…
http://jcreigh.blogspot.com/2006/09/microsoft-censors-msn-messenger.html
and wikipedia article here...
http://en.wikipedia.org/wiki/MSN_Messenger#Censorship_controversy