Case sensitive usernames and sendmail - mystic voodoo

[Modulok]

List,

Step1: Make a new user::

    root at localhost# pw useradd foo -m -s /bin/tcsh -h 0
    password for user foo: (secret)

Step 2: Does sendmail know them::

    root at modunix# sendmail -bv foo at localhost
    foo at localhost... deliverable: mailer local, user foo

    # Good...

Step 3: Make a new user with uppercase 'B'::

    root at localhost# pw useradd Bar -m -s /bin/tcsh -h 0
    password for user Bar: (secret)

Step 4: Does sendmail know them::

    root at modunix# sendmail -bv Bar at localhost
    Bar at localhost... User unknown


Curious, why? I know usernames are case-sensitive, I thought emails were
too. Without fighting an epic battle with with the sendmail configs, is
there a simple way to make this work?

The obvious answer is probably, "usernames should be lowercase!" and for
new users I'll enforce that policy. For existing users however, who may
already have lots of case-sensitive usernames in various config files,
etc this isn't a real option. By just altering their usernames I'm
afraid I'd break the whole damn universe. How can I enable mail for
them?

Cheers!
-Modulok-