Developers of Sympa

[address@concealed]

Hi all,
 
I want to cutomize emails that are sent out by sympa. For example display an
html banner/logo as well as footer for all html emails. 

I tried to do simple customization and it creates 
 message.footer
 message.header
files which are attached to the original message.
 
Instead of attachments, I want to include html content to wrap around the 
email
body

Can anyone help with some ideas? Is it supported by the software ?