$__to =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    $__cc =~ s/(\r\n|\n\r|\r|\n)/\r\n/sg;
    ...

##</code><code>##

my %mail =
(
    "To"             => "$__to",
    "Subject"         => "$__subject",
    "Content-Type"     => $__content_type,
);

##</code><code>##

for ( $__to, $__subject, $__content_type, ... ) {
    tr/\r\n/ /;
    s/\s+$//;
}

my %mail =
(
    "To"             => $__to,
    "Subject"         => $__subject,
    "Content-Type"     => $__content_type,
);

##</code><code>##

my @message_lines = 
  ( '', # blank line
    'This is a multi-part message in MIME format.',
    '','',  # a couple blank lines
    "------=$_random_boundary",
    ...,  # i.e. one array element for every line of message content
    '',''  # including a couple blanks at the end
   );

my $_mail_message = join( "\r\n", @message_lines );