Re: Block No Reverse DNS

Matt said:
> How do you setup Exim to refuse email from MTA's that do not have a valid
> reverse DNS?
>
> I also heard of some hack that allowed you to look at a reverse DNS and if
> it contained *dial*, *dsl*, *cable*, *208-34-34-34*, *204.34.34.34* or
> something like that refuse it since it would likely be a dynamic IP pool.
> Anyone know the trick for that?
>
> Using tricks like this about how much legitiment email do you think would
> be
> blocked?

We used to do that.  Blocked a lot of spam that way... but when I moved
that trait into a large commercial environment, it lasted less than a
week.  Way too many vendors, and other business contacts have questionable
mail servers with poorly configured DNS to whitelist....  I gave up...

But we do use as a scorable item...

# We deny access to hosts that have no valid rDNS
#deny    message = ADMIN BLOCK: This Host does not accept connection
without a valid Reverse DNS Lookup (rDNS)\n \
#       Please contact postmaster@$qualify_domain with any questions.
#        log_message = ADMIN BLOCK: NO VALID rDNS LOOKUP
#         hosts = ! +exempt_lookup_hosts
#         !verify = reverse_host_lookup

# MARK HOSTS WITHOUT VALID RDNS
warn    log_message = SETTING X-NO-rDNS
        message = X-NO-rDNS: No rDNS Found for $sender_host_address
        hosts = ! +exempt_lookup_hosts
        !verify = reverse_host_lookup

Spam assassin has rules to deal with your other issue... DLS pools etc..
though we do have to whitelist some vendors because they fit that too.