[imp] How to change the from format

[Elitec Computer,,,]

Hello everyone,

after installation of imp3 on my debian/woody system
i recognised that writed E-Mails with imp have a from
field like "www-data .. on behalf of" and then the real
E-Mail address. How can i change the from format only to 
show the real E-Mail address ?

Thanks in advance,
Ruediger Pryss