We have emails coming into our server that are then passed on to another server (this is not a virtual server). The server the emails are passed on to is permanently down. We are not allowed to bounce or send any notice back to the original sender. This is causing our mailq to continuously build up with undeliverable mail which I have to continuously delete. I thought the if I put in an 'iptables -A OUTPUT -s 123.456.789.1 -j DROP', that that would cause anything being sent to 123.456.789.1 to be simply dropped. But the mailq is still backing up to this address. I am guessing that postfix is trying to do something ahead of the firewall that is causing this. Any suggestions, rerouting to dev/nul or something like that?

Thanks.

You can't get rid of application data by dropping network packets. The mail server will attempt to deliver mails according to the way it's configured, and by preventing it from contacting the recipient server, you've only ensured that the mails will stay in the queue until they are removed by some other action (manual deletion, automatic deletion with NDRs etc).

You need to reroute mails, not network traffic. Since you're using Postfix, perhaps the method outlined in these articles could be used.

Thanks. I thought that I had discovered my mistake and tried this: iptables -A OUTPUT -j DROP -d 123.456.789.1, but as you have pointed out, that isn't working either.