# ($imap is a MAIL::IMAPClient object already connected to the server)

$imap->Uid(0);
$imap->select('INBOX');
$totalMessages = $imap->message_count();
for my $messageSequenceNumber (1 .. $totalMessages)
{
    my @headerList = ('Message-ID', 'From', 'Subject', 'To', 'Date');
    my $headers = $imap->parse_headers($readMessage, @headerList);
    print "Message-Id is --> $$headers{'Message-ID'}[0])";
}