Removing 'Sender' header from body

[Dani Koesterich <Dani @ MasterMailings . com>]

Hi,

Whenever I send a mailing, a "Sender" header appears on the
first blank line, displaying the sender address. I've tried setting
sender to blank in the .config file, but then mailings just don't work.

Does anyone know how to stop Majordomo from inserting this line
into my mailings?

Thanks!

Dani