#!C:/Perl/bin/Perl.exe -w
use strict;
use Data::Dumper;

my %MailList;  # A list of all seen addresses.
               # This hash is setup in step 1 in the
               # previous post.

# Parse the mail box
while (<DATA>) {
    next unless /^From:\s/; # ignore all other lines
    chomp;                  # except the from line

    # assume that email addresses are separated
    # by the ',' character.
    my @emails = split /,\s*/, substr($_, 6);

    # build a hash from the email address list
    my %emails = map {
                   s/\s+$//g;  # remove tailing spaces
                   my ($name, $address);
                   if (/>$/) { # look for < ... >
                     ($name, $address) = /^(.*)\s<(.*)>$/;
                   } else {
                     $name = $address = $_;
                   }
                   $address => $name
                 } @emails;

    # inspect captured email details
    # print Dumper(\%emails);

    # check if the email address(es) are already seen
    foreach (keys %emails) {
        if (! exists $MailList{$_}) {
            # ok, we haven't seen this Email address yet
            $MailList{$_} = $emails{$_};
        }
    }
}

print Data::Dumper->Dump([\%MailList], ['MailList']);

__DATA__
From: Roger <roger@somewhere.com>, Roger 2 <roger2@nowhere.com>
To: Peter R <peterr@us.com>
Subject: Hello
Hello Peter, this from address has two addresses

From: roger3@somewhere.com
To: Peter R <peterr@us.com>
Subject: Hello
Hello Peter, this from address has no full name

From: roger3@somewhere.com
To: Peter R <peterr@us.com>
Subject: Hello
Hello Peter, has already seen this from address