arros y Triby te han dado prácticamente la solución, si siguieses el enlace de Triby, o buscases
Warning: mail() [function.mail]: Filename cannot be empty te encuentras con esto:
Cita: [2009-03-02 15:30 UTC] kalle at php dot net
Have you enabled the mailing logging feature thats available as of PHP 5.3 and not defined a mail log setting (mail.log)
[2009-03-02 15:45 UTC] jeffreybolle at gmail dot com
Hi Kalle,
Yes that was it my php.ini file had "mail.log = " uncommented by default. Once I removed that line the warning disappeared.
Thank you for your help. Sorry for the bogus report.
Saludos.