In the long run you should quit. What’s the next questionable thing to be asked of you?

For the time being, put yourself in the position of one of the spammees: put your private email on the list and report the received mail to Vipul’s Razor. Report a new IP to the blacklists yourself before it’s used so even the first wave never arrives.

Be sure to take these countermeasures from home or otherwise in your private time, not on company time. Don’t disobey any orders while at work – like by sabotaging the actual spamming itself.

Makeshifts last the longest.