select distinct E_mail from table where <conditions>

##</code><code>##


my %emailhash = ();

foreach $row (result_set) {
  $emailhash{$row->{email}} = 1;
}

my @unique_emails = keys %emailhash;


##</code><code>##

%temp_hash = map {$_ => 1} @non_unique_list;
@unique_list = keys (%temp_hash);

# or

@unique_list = sort keys (%temp_hash);