Are you getting any sort of error message, or does the authentication just fail. My first thought was that it may be the module, but I haven't been able to find any reports of
Net::SMTP_auth, not working on perl 5.8.
Is it possible that each server has a different version of
Net::SMTP_auth. I see that the new version(0.07) uses
Authen::SASL to authenticate and a previous(0.05) doesn't. This is the only thing that I can think off of the top of my head. Your code looks fine to me.