Sendmail Sender Address Validator

This tool is a lightweight, fast and reliable Sendmail filter that implements a real-time Sender e-Mail Address Verification technology. This technology can stop some kinds of SPAM with a spoofed sender's e-Mail address. Also it implements a real-time Recipient e-Mail Address Verification technology. It can be useful if your machine is a backup MX for the recipient's domains or if your machine forwards all e-Mail messages as a relay host for your domains to another internal or external e-Mail servers.

Features:
- external editable configuration file;
- whitelist by an IP address (in CIDR notation);
- whitelist by a PTR (reverse DNS) record;
- whitelist by an envelope sender e-Mail address;
- whitelist by an envelope recipient e-Mail address;
- scalable and tunable fast in-memory cache engine;
- SMTP AUTH support;
- strictly RFC-2821 compliant MX callback engine;
- tolerance against non RFC-2821 compliant e-Mail servers;
- blocking of e-Mail messages with a spoofed sender's e-Mail address;
- recipient's e-Mail address verification with authoritative e-Mail stores (call ahead technique);
- progressive slowdown of recipient's e-Mail address brute force attacks;
- Sendmail virtusertable and mailertable features full support.