Maybe this article will help.http://kb.mozillazine.org/Importing_from_Incredimail

Chuck1 said

I am a new user of Mozilla Thunderbird and would like to know how to transfer email data from (IncrediMail program) to the (Thunderbird email program?) IncrediMail doesn't recognize Thunderbird nor will it allow me to add Thunderbird in the transfer box. I don't want to lose my email data if possible. Hope someone can help. Thanks

Thanks, Airmail for your help. Will let you know how it works. Working with past fixes on other computer programs - it can be hair pulling process.  :) Again thanks. Chuck1

Good luck. Everything I found indicated that Incredimail did not make the switch to another client easy. There were lots of articles when I Googled it.

Airmail - again thanks for your help.