blocking mails from non-existing users

[meyerm]

Hi all,

do you know a possibility to block mails from a non-existing mail account? Speak: Your server gets a mail, checks the existence of the sending account per SMTP (I can't remember how the command is, but there is a special way to verify user-accounts) at the originating server and if there is no such account or even no such server, it simply drops the mail.

Is there anything for qmail or postfix which you are aware of?

Thanks,
Marcel

[kybber]

Have you taken a look at ASK (Active Spam Killer)? I just read about this 15 minutes ago and got quite excited since it's based on an idea I had myself a couple of years ago: ASK will autoreply to mail from unknown senders, asking them to confirm the mail before letting it through to you. After they have confirmed it once they will not need to do so again. Also, you can manually edit whitelists (always let specific mail through) and blacklists (autoreply with a nasty message). It doesn't exactly do what you describe, but you can check it out as an alternative solution at http://www.paganini.net/ask/

[meyerm]

Hi kybber,

thanks for your reply. Your suggestion seems to be an interesting approach for a single user. But my problem is, I'm the postmaster of a small domain with many users. And whenever a spammer sends spam to a nonexisting account on our system, the message is of course bounced. But the mailserver on the other side also bounces since the account doesn't exist. Therefore, all this spam end in my inbox. Also when a user decides to reject/bounce the spam - finally it's mine.

Another problem is spam beeing send with a faked "from adress" of our domain! But this is another topic, perhaps I will start another thread

To summarize: I want the mail from non existing emailadresses immediately dropped (not bounced or sth similar since this will only result in more bounces) and existing accounts pass through. What I do after this gate with the mail is another topic. F.ex. using your ASK or spamassassin or whatever.

Thanks
Marcel

[pan]

You might want to take a look at exim. It can do smtp callbacks and bounce mail (or drop it on the floor) at smtp-time based on any number of criteria. However, you can't really check the existence of user accounts on the sending server in any reliable way, as not all servers (or even most) has the smtp VRFY functionality enabled.

[meyerm]

Thanks, I will have a look at it (perhaps I can even "borrow" some ideas from them and include it into my qmail )

[Larde]

[kybber]

Larde: Thanks for the tip. I'll be sure to check it out