I don't know how to be more blunt about this, but it's a major blunder and every single agent on that list will probably decline your work.
Once a literary agent declines your work, you can not resubmit the work to them unless they tell you what to change and what to send in instead. I'll be honest with you, other than myself... and only because I'm a sucker, most agents might even just delete the e-mail. Or worse, the last time this happened several agents responded with unkind or snappy comments and copied everyone in their response, including the author. I really don't want this to happen to anyone else. Ever!
What did I do this time around? I of course replied the the lovely misinformed author because not only do I feel badly about letting people make such costly mistakes, but also because I saw it as an opportunity to make a difference. I kept it short and sweet. Hopefully he will listen.
My response to the author:
"...I was just about to ask you for a sample of your pages and a synopsis to complete your submission (because the package was also incomplete) for review, but noticed that you copied several agents in this e-mail. In the industry, this is a big No-No. If you don't want to get declined by all of them, I recommend sending an immediate e-mail withdrawing the submission and apologizing for error. Then send them each an independent e-mail following their submission guidelines. I'm only telling you this because your story sounds like it has potential and I don't want you to waste this opportunity to reach good people. Good luck!"
I think that the most helpful thing that I can say here without sounding condescending or preachy is simply to list some of the most elemental, but most important tips you will ever need for Querying Agents.
2- Query each agent separately, very subtlety letting them know that you've done your research by perhaps telling them why you've chosen them. You do't actually need to tell them this. You can simply show them that you've done so by doing all of the things they like and giving them what they want. Use the KISS method- Keep It Simple Stupid
3- Always follow their Submission Guidelines! Most of us have them listed on our websites. If we don't, continue to research.
4- Don't be lazy, be professional, always put your best foot forward. You aren't ready, until you are sure that you've done it right and you're submitting only your best work.
Don't befoul your opportunity to make a good impression... you might not get a second chance!