Nick Howitt wrote:
OK. Let's assume I don't have an MX Backup. Then all 30k+ attempted spam deliveries would have come straight to me. They would all have failed, initially because of unknown recipient, then, when I added them to the access list, because of an denied sender. What is the most efficient way of blocking these messages? Can they be blocked earlier than smtpd_sender_restrictions?
Blocking at that point is still incredibly cheap compared to accepting the message then feeding it to eg SpamAssassin.
About the only notch better you could do would be to watch for some of the IPs, look up the netblock they're part of in WHOIS, then block them in the firewall. That assumes you never ever EVER want to receive mail from anyone using those providers, with ANY domain in the sender address.
I had a P100 with maybe 32MB or RAM, running sendmail, relaying possibly 10-15K messages daily to a legacy mail system running on a Novell Netware 4.something host (yes, really) around 2001, and rejecting a longish list of things based on connecting IP or sender email both within sendmail and occasionally via milter (MIMEDefang). Load was effectively 0. If these aren't showing up in your mailbox, don't worry about it.
-kgd
