Net::SMTP_auth implements a client interface to the SMTP and ESMTP protocol 
AUTH service extension, enabling a perl5 application to talk to and 
authenticate against SMTP servers. This documentation assumes that you are 
familiar with the concepts of the SMTP protocol described in RFC821 and with 
the AUTH service extension described in RFC2554.

WWW: http://search.cpan.org/dist/Net-SMTP_auth/