Mail::Milter::Module::MailDomainDotMX(3pm) on Linux

The text d6faaee1739c, as Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze), Debian 5.0 (Lenny) shipped it.

milter to reject mail whose sender domain publishes a null MX record