Terri,
Check out the ./xtra folder that comes with the ListMail ZIP. These scripts are included by ListMail at certain points in the program IF they are detected in the main ListMail folder.
As per the ./xtra/Readme.txt the signup-xtra.php file can be used to run PHP script after a user is entered into the program. It will run automatically with form and email signup and is optional during manual signup and import.
Could you have copied the files from the ./xtra folder to your main ListMail folder accidentally?
It is safe to delete the signup-xtra.php file from your main ListMail folder to disable it.
Regards