Re: Filtering spam from dialup accounts

[Andrew Stesin <]

On Wed, 13 May 1998, Scott A. Marlin wrote:

> office. What I am looking for are filtering techniques like "no SMTP
> packets can leave InterNeXT if they are from a certain range of IP
> addresses" - I was thinking of a solution on a BGP level.

	Nothing to do with BGP; you need to filter out direct
	SMTP to the world at your external-connectivity interfaces,
	from everywhere but your central mail relay(s) which
	are equipped with antispam filters by definition and probably
	some other trusted relays from inside your customer nets.
	Then convince *all* users to use your relay(s) as an
	outgoing SMTP server, and don't try direct SMTP connections
	to anywhere.

	Pretty simple task, do you need some assistance with cisco ACLs?
	(Talking to users with regard to the above might be much more
	difficult than establishing filters as such).

	This probably also applies to incoming mail.

> Another way of solving the problem would be for *all* other SMTP servers
> to reject mail coming from unresolved hosts. That would help get the
> reverse ARPA up to date. I may just start responding to spam complaints
> in this manner :-)

	Ok the spammer will just send his junk from a backresolved
	address, no big deal for him.


Best regards,
Andrew Stesin

nic-hdl: ST73-RIPE