It may be worth having a look at the SyslogScan package on CPAN - This package can be used to parse sendmail logs and return a wealth of information on mail usage. For example, using this package, your code could be reduced to:

use SyslogScan::DeliveryIterator;
use strict;
 
my $logs = [ '/var/adm/syslog/mail.log' ]; 
 
my $iterator = new SyslogScan::DeliveryIterator( syslogList => $logs )
+;

while ( my $delivery = $iterator->next() ){
    print $delivery->{Sender} . " -> " .
           join( ",", @{$delivery->{ReceiverList}} ), "\n";
}
[download]

This package is also discussed in the sample chapter of the excellent resource "Perl for System Administration" which can be found here.