mail() function

Is anyone familiar with the mail function and how it works on the server? I can't get it to work on a client's server, and this error shows up in the error log: PHP Warning: U1À‰å]Éö¼': Unable to initialize module Module compiled with debug=144, thread-safety=135 module API=1119810252 PHP compiled with debug=0, thread-safety=0 module API=20010901 These options need to match in Unknown on line 0 PHP Warning: U1À‰å]Éö¼': Unable to initialize module Module compiled with debug=144, thread-safety=167 module API=1120015052 PHP compiled with debug=0, thread-safety=0 module API=20010901 These options need to match in Unknown on line 0 If anyone has any suggestions as to what to look for, I would appreciate it. I already tried 'pointing' php.ini directly to sendmail (which is in a traditional spot: /usr/sbin/sendmail). Thanks, -Mike