script that runs all the time to monitor log file

[Chris Lott]

I have a simple little perl program that monitors the email log file for
rejected messages (see below). I start the program using "nohup script.pl &"
and it works fine, sending me an email with info about each rejected
message. However, it just dies out randomly after a day or so for no reason
that I can figure. The script is still there as a process, but it doesn't
perform. 

Is there another way I should be approaching this task?

#!/usr/bin/perl

     $maillog = "/var/log/maillog";
     $TAIL = "/usr/bin/tail";

      open(MAILLOG,"$TAIL -f $maillog |") || die("Can't $TAIL -f $maillog");
        while($line = <MAILLOG>) {
        if ($line =~ /blocked/) {
       system("echo '$line' | mail -s 'RBL rejection' foo\@bar.com");
        }
     }
     close(MAILLOG);
     exit(1);