The other half of this is if you are on VZ's network and try to send
mail through their system, you cannot unless you have a "verizon.net"
from address. Or at least that was the case when my friend with VZ
DSL tried to send e-mail through VZ from her personal domain.
IOW, VZ isn't even checking to see if a zombie'd host is forging its
own domain into HELO, regardless of whether it comes from Comcast or
UUNet, and as long as the forged sender has a verizon.net address, and
the recipient hasn't blocked VZ's silly callback system, the message
is relayed. Thanks, Verizon. We can hear you now.