sub logger {
    my $entry = shift;
    my $logpath = 'C:\\Logs\\MailServer\\';
    my ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime;
    my $datestamp = sprintf '%04d_%02d_%02d', 1900+$year, 1+$mon, $mday;
    my $timestamp = sprintf '~<%02d:%02d:%02d>~', $hour, $min, $sec;
    my $logname   = $logpath . $datestamp . '.log';
    my $logline   = $timestamp . $entry;
    if (defined $entry) {
        open my $LOG, '>>', $logname or die "open: '$logname': $!";
        say $LOG $logline or die "say: '$logname': $!";
        say $logline;
        close $LOG;
    }
}