mail function fails with no error code

I am unable to send emails, and there are no errors being generated or populated in the $php_errormsg variable, since I enabled track errors in the php.ini. So I have no idea why the mail send is failing. Am I supposed to specify a mail server to use for sending mail? My sendmail was setup automatically in my Redhat Setup and I have not touched its configuration options...is there something I need to change? The sendmail path that is shown in the phpinfo() function display is correct. Any feedback would be greatly appreciated. Thanks! -M L