open( USRS, "users.txt" ) or die "no users.txt: $!";
my @emailStrings = <USRS>;  # let's just read this once
close USRS;

foreach ( keys %postiniList ) {
    if ( exists $ldapList{$_} ) {
        print "$_ exists in ldap\n";  # don't need a "next;" here
    } else {
        print "$_ does not exist in ldap\n";
        my ( $match ) = grep /\Q$_\E/, @emailStrings;
        my $emailString = ( split /\t/, $match )[1];
        print "deleteuser $emailString\n"
    }
}