#!/bin/perl -w 
use strict; 
  
my $file = "xxx"; 
my $pat = "<!--mailto:-->"; 
  
open FILE, $file    or die "cannot open '$file': $!\n"; 
my @lines = <FILE>; 
close FILE; 
  
my @sorted = sort grep { /^$pat/ } @lines; 
  
open FILE, ">$file" or die "cannot open '$file': $!\n"; 
print FILE map { /^$pat/ ? shift(@sorted) : $_ } @lines; 
close FILE;