Try something like the following (untested) code:

use Mail::Bulkmail;

my ($subject, $message);
open(MSG, "message.txt"); 
while (<MSG>) { 
  if ($_ =~ /^[Ss]ubject:\s*(\S*)/) { 
     $subject = $1;
  } else { 
    $message .= $_;
  }
} 
close MSG;

my $bulk = new Mail::Bulkmail(
        Message      => $message,
        Subject      => $subject,
        From         => 'Home',
        LIST         => 'email.txt'
        use_envelope => 1,
);

$bulk->bulkmail();
[download]

If you have an older version of Mail::Bulkmail than you can simplify this even more by using the HFM (Headers From Message) feature that has dissapeared from version 3.x.

use Mail::Bulkmail;

open(MSG, "message.txt"); 
undef $/;
my $message = <MSG>;
close MSG;
 
my $bulk = new Mail::Bulkmail(
        Message      => $message,
        From         => 'Home',
        LIST         => 'email.txt'
        use_envelope => 1,
        HFM          => 1,  # pull headers from message
);
[download]