/etc/exim4/exim4.conf.localmacros is:
DKIM_DOMAIN = jazz2.eu
DKIM_SELECTOR = x
DKIM_PRIVATE_KEY = /etc/ssl/private/dkim.private.key
DKIM_CANON = relaxed
newline characters are immediately after the text on each line ... I was suspecting a macro parsing error after I noticed exim not recognising the last line until I added a null last line
update-exim4.conf picks these macros up OK and generates a /var/lib/exim4/config.autogenerated with the macros embedded
however, emails sent after restarting exim report that the private key file cannot be read