To: GetADiplomaOnline
Content-Type: multipart/alternative; 
              boundary=be638aa04b654852d0173c0e3f9b6d20
From: some@email.address.co.uk
to: @huge_list_of_email_addresses

##</code><code>##

my $email = Email::Simple->new($email_text);
my @headers = $email->header('to');

##</code><code>##

'header_names' => {
  'content-type' => 'Content-Type',
  'to' => 'To',
  'from' => 'From',
  'subject' => 'Subject'
},
  'order' => [
  'To',
  'Content-Type',
  'From',
  'to',
  'Subject'
]