Another approach is shown below. Basically you are trying to find out if the @all array is a subset of each of the dlist arrays. I assumed that perhaps the dlist array might contain more e-mail addresses than the @all array.

This type of "check off the list" comparison is often done with hash tables. My comparison function makes a hash out of the dlist from the HoA. Then it iterates over each e-mail in @all and "checks off" in the hash as each one is "seen". If I find a e-mail address from the @all list that isn't in the array from the dlist hash, then it can't be a subset and the function returns a failure (not a subset).

Once it has been determined that the dlist (like "listC") contains all of the e-mail addresses in all, I count up any "extra" ones and return that list. This would allow say the compression of "listC" to be "all@foo.com, billy@foo.com".

A noteworthy point here is how returning the @extra array was handled. I return () to mean "nothing", NOT undef. undef is a value. Returning () means "nothing" which is "less than" returning an undef value. The first time I did this, it took me many hours to figure out how to do it! So at some point in the future just having seen this one point may save you a lot of grief! Have fun...

#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my@all = qw(bob@foo.com  joe@foo.com jane@foo.com);
            

my %dlists = ( 'listA' =>[ qw (bob@foo.com  jane@foo.com
                              joe@foo.com) ],
               'listB' =>[ qw (bob@foo.com)],
               'listC' =>[ qw (bob@foo.com joe@foo.com 
                               jane@foo.com billy@foo.com)],
             );

foreach my $dlist (keys %dlists)
{
   my ($subset, @extra) = is_array_subset(\@all, \@{$dlists{$dlist}});
   if ($subset)
   {
      print "$dlist contains all users ";
      if (@extra)
      {
             print "and ".@extra." additional addresses\n";
      }
      else
      {
             print "\n";
      }
   }   
}


sub is_array_subset   #returns (yes|no status, @extra)
{
   my ($ref_all, $ref_dlist) = @_;
   
   my %dlist = map{$_ => 0 }@$ref_dlist;
   
   foreach (@$ref_all)
   {
      return (0, ()) if !exists($dlist{$_}); #give up! not subset
      $dlist{$_}++;
   }
   
   my @extra = ();         #is subset, now see if any "extra's"
   foreach  (keys %dlist)
   {
      push @extra, $_ if $dlist{$_} == 0;
   }
   
   return (1, @extra);
}

__END__
prints:
listC contains all users and 1 additional addresses
listA contains all users
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