sendmail not authenticating with smart host

[Derrick Ryalls]

Greetings,

Due to port 25 restrictions, I am trying to get my brother's email
server to authenticate out on port 587.  I have sendmail talking via
port 587, but it is not properly authenticating.  To help narrow
things down, I am having his machine route all mail to my machine with
authentication.  His machine is a running version 7:   7.0-RELEASE
FreeBSD 7.0-RELEASE #0: Sun Feb 24 19:59:52 UTC 2008

Here are some relevant parts of the hostname.mc file:

define(`SMART_HOST', `myserver.com')
define(`confAUTH_MECHANISMS', `LOGIN PLAIN')dnl
FEATURE(`authinfo',`hash /etc/mail/auth/client-info.db')dnl

auth/client-info has this:

AuthInfo:myserver.com "U:hisuser" "I:hisuser" "P:password" "M:PLAIN"

And I have created client-info.db hash.  I have copied the config file
workflow from my server which uses smtp auth to talk to my ISP on port
587.

On myserver.com, I do see that his machine connects to me, but I see
this error in maillog:

Relaying denied. Proper authentication required.

When I was trying to go through his ISP, I got this error message in
his error log:  stat=Service unavailable.  We share ISP (from
different states though) and I am still able to send via my ISP.  I
even tried to directly copying my auth info for the ISP from my box to
his (so he would be sending as me) and I got this same error.

Have I missed a configuration setting somewhere?