You can code your script to do either. I suggest you figure out why your emails are being flagged as spam and fix the problem. Usually, the negative points about you are easily fixable by setting your email headers properly.
If you have an array of email addresses, you can either concatenate all your users into a single To: field, or iterate over each user and send the email to them individually.
Take care,
Nik
http://www.bigaction.org/