Configure sendmail to reject mail for unknown users?

[Timothy Alberts]

So after many helpful responses (thank you everyone), it sounds like I
should change how I use the access file to something like:

mydomain.com REJECT
validuser1 at mydomain.com OK
validuser2 at mydomain.com OK
validalias1 at mydomain.com OK

This will supposedly reject any email address (account and/or alia) that
I don't explicitly list as OK.  However, the following excerpt
from /etc/mail/sendmail.mc seems to say that the way I'm using it is the
correct way and this modification wasn't the original intention:

dnl # With blacklist_recipients you can add entries to the map (access
file) for local users, hosts 
dnl # in your domains, or addresses in your domain which should not
receive mail
dnl # for example: oldemployee at mydomain.com	ERROR:550 Mailbox disabled
for this username
FEATURE(`blacklist_recipients')dnl

This makes me nervous.  Any comments?  Again, I'm not using the virtual
users, it is the only server for the domain, I only have one domain, and
the server has all the accounts in it.