Well, forget it. Many major providers like Yahoo, AOL, Hotmail etc.pp.
have *VERY* SPAM strict filters in place. Especially if you use Bcc:'s,
chances are high that a lot of your will bounce.
If you'll be doing something like this more often, it'll be a lot easier
and a lot more successful if you outsource this to specialized
companies. They know how to circumvent this kind of trouble.
Or install your own listserver software.. I'm not sure how good they are in terms of using a MySQL database as source, but you could create any file using PHP..
Might be worthwile to check this.. also.. these packages would normally handle bounces. You could do the same but it would cost you to much time.
Bye,
B.