"formail" query

Hi,

I would like to generate an automated reply to the sender, how should 
I go about?

I have edited the rc.maillists file such that the content is as 
below:
:0:
* ^From(_dot_)*(_at_)tp(_dot_)ac(_dot_)sg
| /usr/lib/sendmail sinsoon(_at_)tp(_dot_)ac(_dot_)sg

Is there any way whereby I could add-in the formail command here?

Thanks in advance