mxallowd is a daemon for Linux Netfilter (using libipq) which implements a slightly improved nolisting mechanism. It requires your name server to be configured to return two MX IP addresses, and the one with higher priority must not run a mail server on port 25. mxallowd blocks attempts to connect to the mail server unless the sender tries to connect to the first mail server before the second. Since most spammers will attempt direct connections to each mail server, they will be blocked. License: GNU General Public License v2 Changes: mxallowd now supports IPv6.

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