[PLUG] Why some sites no PTR record???

[Michael C. Robinson]

Ebay, St Helens Community Federal Credit Union, ...

Question I have, why aren't these email sources reverse resolvable?

How on Earth am I supposed to detect that a mail host is a random
infected personal computer instead of some domain's legitimate email
server?

Should I go ahead and block if there's no reverse PTR record?

Short of saying there is a resolution problem and requiring that
another message be sent with a secret I provide for white listing
purposes, what can I do?

Since I have the email connection request packet in user space, can
I do something to the packet to cause Postfix later to bounce it?