Text can be inserted below a new reply or forward. However, HTML requires complex parsing and therefore isn't currently included but if you switch to text mode you should see the text version of this.
We are working on a new fully web based Ability Mail Server 3 at the moment which will include a full admin and webmail interface re-write using database settings with entity framework, .net 4 and ASP.Net MVC 2 (new feature only just out this year). If not in the first version of the new WebMail I'll try to get a HTML parser for WebMail included in an AMS 3.xx update.
Ability Mail Server 3.xx won't be complete until the end of 2011 at the earliest. However, we're releasing another update for Ability FTP Server 2 and Ability Mail Server 2 in the coming weeks. Ability FTP Server 2 update should be out later this week hopefully. You can join our mailing list at
http://www.code-crafters.com/mailinglists.html to be informed when new updates are released so you can stay up to date.