Which version of ActivePerl is this? I'm looking at Net/SMTP.pm from (64-bit) ActivePerl 5.18.2, and sub mail has a number of cases where it can carp(). Do you see any warnings? What does "crap out" mean in this case? Turning on Net::SMTP debugging as marto suggests might reveal whether the problem comes from argument processing in sub mail, from sending the MAIL command to the remote server or parsing the response from the remote server.