Forum Moderators: phranque
In terms of mitigating the damage;
1) Put a notice up on your site which links to a detailed explanation of the problem - you might be able to work out the true source using one of the bounces and something like spamcop (but I wouldn't bet on this).
2) Handle any complaints nicely (even when they are not being nice themselves), possibly referring them to the page you created for (1).
Aside from these its just a case of sit & wait
- Tony