Unknown users

[Mike]

Hi,

Just wondering if anyone can answer my query?

Having recently installed Qpopper, I'd like to set up an auto-reply 
text file, for informing those people who send email to ALL UNKNOWN 
email addresses/users that the address does not exist/user unknown.

EG Local or internet email addressed  to [EMAIL PROTECTED] 
should get an email saying "Sorry that user is unknown, email 
returned"

How do I go about that?

Many thanks for all your help and advice.

Mike