[exim] BATV and closed mailing lists

Hello List,

I have setup a closed mailinglist following:

    http://www.exim.org/exim-html-current/doc/html/spec_html/ch49.html

However one member's mail provider uses BATV, which changes his return-path to
something like

    Return-path: <prvs=123456=foo@???>

while his email address is really:

    foo@???

With that the

    senders = ${if exists {/usr/lists/$local_part}\
                 {lsearch;/usr/lists/$local_part}{*}}

fails, and he can not send mail to the list.

How can I solve this?

Thanks,

    Stefan
-- 
BOFH excuse #248:

Too much radiation coming from the soil.