A bit OT: Cut off address probes?

[Ken Anderson]

Furnish, Trever G wrote:

> This is probably a bit off-topic, and I hope it's not a faq somewhere
> already - feel free to yell at me constructively if so. :-)
>
> Is there a way to configure sendmail (or whatever) such that "address
> probes" are less effective and intrusive?  I could imagine how the process
> might work, but I've never coded a milter and am hoping someone else has
> done this or will tell me why it would be a bad idea.
>
> By address probe, I mean connections that either:
>         1. Ask the receiving mta to accept a message for one invalid address
> after another despite repeated negative responses from the receiving mta.
> Something that amounts to "Is bob valid?" ... "no"  ... "Well, what about
> tom?"  ... "no"  ... "Frank?" ... etc.

See http://www.sendmail.org/m4/tweaking_config.html#confBAD_RCPT_THROTTLE

>         2. Send a message with many recipients at the same server, learning
> those that don't bounce.
>
> Completely blocking "no such user" responses seems like a bad idea, but
> ignoring someone who attempted delivery to X number of invalid addresses
> within Y seconds seems like a good idea.  But how can the first-line MTA
> know whether or not an address is invalid?

You have to tell it.
Use access db with blacklist recipients.
See:
http://www.sendmail.org/m4/features.html#blacklist_recipients
Ken

> Has anyone set up or read of such a system?  Perhaps a sendmail milter that
> looks up recipient addresses in a flat file or via ldap before accepting the
> message?
>
> --
> Trever
>
>