[Mailman-Users] exim4 + mailman on debian...unrouteable addresses?

[shawn]

i have a problem with this set up. i've searched and searched all over
and can't find a useful solution.

i have followed these documents

http://www.debian-administration.org/article/Mailman_and_Exim4
http://www.debian-administration.org/articles/140
http://www.exim.org/howto/mailman21.html

exim4, procmail and maildir are all working fine. but, when we create
a mailman list and try to send to the list (e.g. mailman at example.com)
i receive an error saying the user/address is unrouteable?

web:~# exim4 -bt shawn at example.com
R: system_aliases for shawn at localhost
R: userforward for shawn at localhost
R: procmail for shawn at localhost
shawn at localhost
   <-- shawn at example.com
 router = procmail, transport = procmail_pipe
web:~#

but...

web:~# exim4 -bt mailman at example.com
mailman at example.com is undeliverable: Unrouteable address
web:~#

i have been banging my head against this for two days now and i can't
find anything that makes sense online?

any ideas?

do i need to add a "user" alias in each /etc/exim4/virtual/...
configuration? if i do that, then the mail delivers to what ever local
user i alias, but it won't post to the list?