On Wed, 27 Mar 2002, John Horne wrote:
> PLYM_NET = 141.163.0.0/16
> ISP = 194.164.0.0/16
>
> hostlist external_hosts = ! PLYM_NET : ! 127.0.0.0/8
> hostlist rbl_hosts = +external_hosts : ! ISP
That won't work (as you have found). Remember that if a host list ends
with a negative item, there is an implicit : * at the end.
> If I set the
> helo_verify_hosts to '! PLYM_NET : ! 127.0.0.0/8 : ! ISP' then that works
> fine too.
Exactly. When you wrote
helo_verify_hosts = +external_hosts : ! ISP
it is in fact equivalent to
helo_verify_hosts = ! PLYM_NET : ! 127.0.0.0/8 : * : !ISP
which is why it didn't behave the way you expected.
Or, to look at it another way, when Exim is processing rbl_hosts, it
first asks "Is the host in +external_hosts?" The answer is "yes", because
it matches
! PLYM_NET : ! 127.0.0.0/8
(because of the implied * at the end). So Exim never looks as ! ISP.
This seems to be one case where using a macro instead of a host list
would be more intuitive. (And I thought it was all the other way round!)
Negation is always tricky, unfortunately. How about doing it the
other way round? For example:
hostlist internal_hosts = PLYM_NET : 127.0.0.0/8
hostlist rbl_hosts = !+internal_hosts : ! ISP
This will also continue to work when you change PLYM_NET to contain more
than one item.
Maybe I should document somewhere the best way of reading these things:
a : b a or b
!a : b not a and b (or b and not a)
!a : !b not a and not b
After a positive item ":" is "or"; after a negative item, it is "and".
So your setting or rbl_hosts means "external host or not ISP", which is
isn't what you want.
I hope this helps!
Philip
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
