[Mimedefang] Re: Soliciting opinions on filtering based on bad MX records

[Jeremy Mates]

* David F. Skoll <dfs at roaringpenguin.com>
> You should also check for multicast addresses (224.x.x.x, and up, I
> believe).

RFC 3330 covers "Special-Use IPv4 Addresses"

http://www.faqs.org/rfcs/rfc3330.html

multicast is 224/4; the 240/4 range above that was unallocated, last
I checked.

> > (2) If the MX record exists, I test it to see if it's in the format
> >     of an IP address.
> 
> It shouldn't be; according to the RFC's, an MX record must be a host name,
> not an IP address.

Except for various rfc-ignorant or otherwise misconfigured hosts...