Well, you can send data in RTF or RVF format, but it is not recommended, because these formats add too many additional information to text, and traffic will be increased.
I recommend to invent some simple language to encode formatted text.
For example, it can be like in this forum, e.g. [b]bold text[/b], or invent your own codes.
Example is here:
http://www.trichview.com/forums/viewtopic.php?t=63
In this example, codes are typed in TEdit (with preview in TRichView).
If you want an example where formatted text is typed in TRichViewEdit, let me know, I'll create a demo.