[Exim] Lookup in flat file failing

Hi,

look at this:

# grep host_reject /etc/exim.conf
host_reject_recipients = +allow_unknown:/etc/exim/blacklist

# grep 195.65.227.21 /etc/exim/blacklist
195.65.227.21

# exim -bh 195.65.227.21

**** SMTP testing session as if from host 195.65.227.21
**** Not for real!

>>> host in host_lookup? yes (0.0.0.0/0)
>>> looking up host name for 195.65.227.21
>>> IP address lookup failed
>>> host in host_reject? no (option unset)

I don't quite understand why this fails.

Ciao,
        Martin