> From: MX%"email@example.com" 18-MAR-1996 10:12:35.42
> Subj: Re: mailing list spams
> >>There is one thing that I've been meaning to look into though. Sendmail -
> >>the most used MTA on the Internet blindly accepts mail from anybody for
> >>anybody. I want to put an end to this. I've been meaning to look into how
> >>much work it would be to make Sendmail refuse to accept a peice of mail not
> >>destined for a user of any of the domains it is serving. (i.e. the
> >>contents of the "w" macro).
> >Can't do this without changing the standard first -- this is a defined
> >feature of SMTP-based mail systems. Probably hopeless.
> This is true, but...
> Nothing stops you from refusing SMTP connections from domains which
> harbor spammers. I wonder how the typical provider would handle:
> - being told that their domains were refused service, and
> - all the complaints from their legitimate customers who
> get served off lists as a result.
I believe that there are some new reply codes in a later SMTP
RFC that address this, but I'd be hard pressed to say which one without
a couple of hours of research...
I did actually hack my mailer once to refuse connections from a
mail bomber, until I could contact his ISP and have his account closed.
> The package you're looking for (if you want to do this) is tcpd;
> earlier incarnations were known as tcp_wrapper.
BUT, this does not handle the case if you have an offsite MX
backup host, unless you control their SMTP access as well. If the
sending host cannot connect to you, it'll fail back to the secondary MX
host, which will happily deliver mail to you...