[support] Mass E-Mail in Drupal 7

Dear All I have some doubt regarding mass email in Drupal. Lets say I want to send mass email to 5000 users at a time from a custom module.

In custom module, I have to make use of drupal_mail() to send email. Now do I need to loop through 5000 times and send the mail, or is there any way I can send mail to 5000 users.

Can I put 5000 email ids in CC or BCC . If so, with drupal_mail, how can I put the mail ids in CC or BCC list. Is there any limit how many email ids I can put in CC / BCC.

Note: Once I tried to sending 3500 mails, in a for loop. Each email id I did put in to field. Looks some of the users did not get email. I am wondering what is wrong and why some users did not get mail.

Thanks kamal