Rule of thumb: If you can see ANY typeface features -- color, bold, italics, big/small letters, etc you have non-plain-text features turned on.
here is their reply : We used to allow only plain text but when aol/MSN and others dropped the capacity for text only messages to be sent by their software, we had to allow them too, or we would have "cut off" 30%-50% or so of our members.