SMTP headers

Hello,

we currently use a RTE (Reliable Transport Engine) to send emails 
containing attachments. Although the attachments appear within the 
e-mails' bodies as icons, in "heavy" mail clients, such as Lotus Notes, 
Apple's Mail, etc., they don't show up in "light" mail clients such as Web 
mail clients (www.excite.com, www.free.fr, etc.) By comparing SMTP headers 
sent by our RTE and those sent by Mutt on Linux, I have noticed that the 
former sends "attachment" headers which don't contain the attachments' 
contents :

...
--------14507F4DC80F4D6511158149340B40B01
Content-Disposition: attachment; filename="test.txt"
Content-Transfer-Encoding: 7bit

Content-Type: Text/Plain


--------14507F4DC80F4D6511158149340B40B01
...

whereas the latter sends "attachment" headers containing the attachments' 
contents


--------14507F4DC80F4D6511158149340B40B01
Content-Disposition: attachment; filename="test.txt"
Content-Transfer-Encoding: 7bit

Content-Type: Text/Plain

This is the contents of the file
--------14507F4DC80F4D6511158149340B40B01

Does anyone know how to force RTEs or MTAs such as sendmail to send 
"attachment" headers of the second kind?

Many thanks.

Best regards,

Philippe