Hi all
after some diggin' in the net and old mailing lists, I solved it as
follows:
(...)
badusers:
driver = domainlist
domains = customer1.org:customer2.com
local_parts = lsearch;/etc/exim/badusers.${domain}
route_list = * localhost byname
self = local
verify_only
local_domains
driver = domainlist
transport = local_smtp
route_list = customer1.org c1mail1:c1mail2 byname;\
customer1.org c2mail1:c2mail2 byname
(...)
Now there exist files /etc/exim/badusers.customer1.org and
/etc/exim/badusers.customer2.com that contain entries like
foo: :fail: No such user here
bar: :fail: No such user here
...
-- Ben (tictactux at surfeu in ch)