tricks including "hash busters." The DMA will soon finish passing
laws in all major jurisdictions that criminalize header forgery as
the first step in saving "push advertising". (The other jurisdictions
can be blacklisted by IP address.)
How do those laws define header forgery? As discussed here,
legitimate header forgery is extremely common. Individuals forge
headers to point at their other email accounts. Companies forge
headers to point to addresses that deliberately bounce (particularly
email from their abuse auto-responders).