bouncing unknown addresses

[Eric Long]

I have a domain name similar to another domain name registered by another
company.  It appears that their users have no regard for how to correctly
type their own domain name, so they forget one letter and end up sending
mail to a nonexistant user on my system.  I would like to bounce any
misdirected messages back to them instead of having them all land in the
postmaster account.

Any help would be appreciated.

-Eric