Group names should be checked, the character ":" should not be allowed in a group name. This is the right delimiter for addressing micro-blogging messages. I created for example two groups named "test" and "test: x". It is not possible to send your message to "test: x" using the "@xxx:" syntax. Since it's confusing, I suggest to not deal with this ":" character at all in group names, and just forbid it. For now I don't see what other characters could be forbidden... I checked for trailing spaces, they are already removed from the name and that's OK.