[anti-spam-wg] Domains with MX set to localhost

[Yiorgos Adamopoulos adamo@localhost]

Hello!

The past few months I observe a trend to have spam directed to us where 
the sender's domain has as MX either the localhost or 0.0.0.0.

As an example the domain yahho.gr (:-) has as MX mail.yahho.gr which 
resolves to 127.0.0.1.

Do you block such domains?  Do you maintain a list?

./Yiorgos