I use this script to test webapps using mail with this little php script saved as /usr/sbin/sendmail : 
#!/usr/bin/php
<?php
    //====================================================
    // Program : Fake send mail
    // Author : pouletfou at gmail
    // Description : save this file as /usr/sbin/sendmail
    //  and you can test your PHP applications using mail
    //  by looking at the /tmp/fakesendmail.log files.
    //====================================================
    define('LOGFILE','/tmp/fakesendmail.log');
    $log = fopen (LOGFILE,'a+');
    fwrite($log,"\n".implode(' ',$argv).
     " called on : ".date('Y-m-d H:i:s')."\n");
    fwrite($log,file_get_contents("php://stdin"));
    fwrite($log,
"\n===========================================================\n");
    fclose($log);
?>
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