Anyone know to get purchase orders approved/rejected using email alone? i.e. sending an email out with Approve/Reject buttons in the body?

I don't that is possible natively.

yes, probably, there's little to no info on it, some are so "busy" that they can't be bothered to log into NS and click approve

Advanced Approval maybe...

You can do it with a script. Advanced Approvals Bundle has that functionality also

Thanks