I really do not know the difference between the term "identity" and the term "account". My Thunderbird has three different email addresses that it collects messages into. I can receive or send from all three separately. The problem is that all emails from my business (comcast.net) account show up as a duplicate in my personal account (a gmail account). Oddly, those same messages do not show up in the third account (comcast.net). What am I doing wrong? Thanks for any help!