[exim] ISP recently updated exim via DirectAdmin

My ISP uses the

SpamBlockerTechnology* powered exim.conf, Version 4.5.26

and now since that upgrade on Friday none of userforward stuff works.

it all still looks pretty standard.

userforward:
driver = redirect
domains = lsearch,ret=key;/etc/virtual/domainowners
allow_filter
check_ancestor
check_local_user
no_expn
file = $home/.forward
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply
directory_transport = address_directory
no_verify

How can you debug a problem like this where you want to know why userforward has no affect?

R=userforward no longer appears in the mainlog file.