I recommend 

a) get the O'Reilly sendmail book

and 

b) use the .mc preprocessing.

On Fri, 2 Feb 2001 wojtek@wojtek.from.pl wrote:

> if someone understand sendmail.cf enough to write his own parts in it
> (without .mc preprocessing) and want to help please mail me. i need to add
> some simple feature to sendmail without stupid hacking it's C code which
> is not only badly working bad not portable to new versions.
> 
>