Lower tech than email spoofing, but.....
Many years ago, working at a large warehouse/office complex, some of us got very irritated with our useless boss call diverting all his calls to our phone.
Several plans of revenge were put into motion, but the one with the biggest impact occurred one night; while dodging the security doing rounds, we managed to access about 70-80% of all the phones in the complex and diverted them to our bosses phone. (The system wouldnt allow a diverted call to be diverted a second time).
I understand he is still trying to stop Readers Digest, Everest, CO-OP Funeral Services and a few other companies from sending him sale reps though.
(Spent another night filling in packs of Rep request cards from a trade show)