[Mailman-Users] router/aliasing problems with exim4?

[Andrei]

I have a problem sending emails to and from mailman lists. I think the
problem is with the router setting, or perhaps with mailman not
creating aliases for the lists.

Mailman is installed and its website loads fine. I can manage, add
lists, and do other admin tasks
However, when I try to send an email to test at lists.host.org I get an error.
If I send an email to user at lists.hosts.org email works fine. I can
send and receive emails as a user, but not as a list.

Is there a log that I can use/monitor to trouble shoot this?

This is my router setting:

begin routers

  mailman_router:
    driver = accept
    domains = +mm_domains
    require_files = MM_LISTCHK
    local_part_suffix_optional
    local_part_suffix = -admin     : \
 -bounces   : -bounces+* : \
                        -confirm   : -confirm+* : \
 -join      : -leave     : \
 -owner    : -request   : \
 -subscribe : -unsubscribe
    transport = mailman_transport