mail() only working with php-cli

Is there any way to debug the mail() function within PHP4 or PHP5? The following code is not working when called from a browser, but it does work from the command line: <?php $to = 'my@self.com'; $subject = 'the subject'; $message = 'hello.......'; $headers = 'From: foo@bar.com' . "\r\n" . 'Reply-To: foo@bar.com' . "\r\n" . 'X-Mailer: PHP/' . phpversion(); if(mail($to, $subject, $message, $headers)) echo "IT WORKED"; else echo "DAMN!!!"; ?> php and php-cli use the same php.ini file. Php via Apache is launched as a module, NOT as CGI! sendmail_path is correctly set to /usr/sbin/sendmail -t -i the /var/log/mail.log only shows activity when I try my code via command line, so my best guess is that sendmail is never reached when run from the browser. I went a little deeper and modified the sendmail_path to /tmp/test.sh, which contains: #!/bin/bash echo "I was used!!" > /tmp/test.log (chmod 777 /tmp/test.sh) Again I tried my script from the web and from the command line. Same result... command line is fine and generates the test.log file. In the browser no log file is created. I have already made numerous LAMP installations, but I never had this kind of mail() issue. This installation is quite simple: standard Apache 2.0 with php5, php5-mysql, php5-gd, ... This makes it even more frustrating :-( What am I missing? Thanks a lot!! ---- Andy