Re: [Exim] HELO acl

On Sun, 30 Mar 2003, Giuliano Gavazzi wrote:

> I did implement 3/4 initially, where a certain sender/helo pattern
> would trigger a check of the reverse DNS against the domain in the
> helo. Tricky when you consider country domains (each one with its own
> organisation of domains at the second or third level). Also it really
> is against RFC, where the only requirement, it seems, is that the
> helo argument resolves to the ip address of the host.
> I then perfected this by checking the direct DNS of the helo arg
> against the ip of the host, if the reverse DNS check failed. I
> consider this an RFC enforcement.
> I estimate that these checks cut spam by over 95% (no RBLs!).
> Unfortunately, thanks to some cleverly misconfigured hosts, some
> legitimate email were also rejected. In one case it took me a over a
> month to get their DNS fixed, in most cases I did not manage to get
> anything done.

And again, this isn't a perfect solution, what about hosts with two
outgoing interfaces?

primary_hostname is set to the hostname of the first interface, but
sometimes the host sends with the second interface (I think this isn't
very unusual).

Nico