[exim] Tainted filename on DKIM signing in 4.94

Hi all,

I have the same issue as reported here:

https://lists.exim.org/lurker/message/20200606.112240.9ecf1e56.en.html

But I'm too thick to undestand if the solution posted can be applied to
my setup as it looks a bit different:

remote_smtp:
driver = smtp
dkim_domain = ${sender_address_domain}
dkim_selector = dkimxy
dkim_private_key = ${if exists \
{/usr/local/etc/exim/${sender_address_domain}/dkim.private.key}\
{/usr/local/etc/exim/${sender_address_domain}/dkim.private.key}\
{false}}
dkim_canon = relaxed

I'm unsure if this is the case on the other thread, but my requirement
is to choose the key based on the sender domain so as to support unique
DKIM keys for multiple domains. Can anyone advise?

thanks in advance,

Andy.