Approving Majordomo posts

[Fraser Campbell <fraser@baxter.net>]

We have a customer who needs to send HTML emails to a mailing list they
have.  The majordomo approval mechanism that I have always used is to put
"Approved: password" followed by a blank line as the first line of the
message.

However, when writing HTML emails, the "Approved: password" will no longer
be the first line of the message since various HTML codes and/or MIME-type
messages will appear before the actual text.  This is the problem I am
having.

The other approval mechanism I know of is to put "Approved: password" as a
mail header.  I have tested this using mutt and it works fine.  Now the
problem is that none of the graphical mail clients (for MS Windows) seem to
offer the option of adding a custom header.  A person I work with was able
to make Microsoft Outlook do this by creating a new email form, it worked
fine but I don't want to tell the client(s) that they have to use Outlook
and then they have to customize the form they use to compose their mail.

So my question is, are there any mail clients (for MS Windows) that can
create HTML emails and offer the option of adding customized mail headers? 
If this is not the case, are there other (the easier the better) options
for sending the approval password?

Thanks,

Fraser