Pkg exim4 users - Aug 2010 - Can exim show its expansion for @?

? Is there a way to exim4 -bP @?
exim4 -bt local_user@$(hostname -f | cut -f 1-4 -d ''.'')
succeeds only
when I explicitly add $(hostname -f | cut -f 1-4 -d ''.'') to
/etc/exim4/update-exim4.conf.conf:dc_other_hostnames.
? exim4 -bP +local_domains does have @ as its first component.