An autoresponder software placed on your server might work. This way you could both send out the emails and verify them at the same time. Of course, this could also get your server/site blacklisted as well.
Why not choose a bulk email marketing software, which will save time and enery to do that. If you want to know more,you can go to iKode newsletter server, which may be a hand for you in doing business in the future.
you need and email service provider there are couple of big names like mailchimp, icontact but if you want a reasonable email maketing service provicer with 24/7 support then visit our service <snipe>. Hope you will like it.
If Mozilla Thunderbird can't help you with that by importing the list and sending out via bcc, then a bulk email service would be more appropriate. I am subscribed to mailchimp, though I have not reach a list of 99999 so I can't tell if they can handle that.