Perl code (QPP) fix

I purchased the perl/cgi code for the "Quick Pay Pro" software in 2002. The application worked fine until I had a programmer make some enhancements 2 years ago. Now when trying to send eMails to large lists, the software duplicates that list 10 to 12 times, so the end user receives the same message in his/her inbox 10-12 times. The problem I believe is in the "[login to view URL]". I need a coder that is familiar with looking at other developers code and find the problem. Familiarity with the Quick pay pro" software v 2.95 (in perl) is a big plus.