A note on sending bulk emails:
If the email you are sending is not personalized, consider using the
"undisclosed-recipient:;" strategy. That is, put all of your recipients
in the Bcc field and set the To field to "undisclosed-recipients:;".
It's a lot faster (only one send) and saves quite a bit on resources.
Contrary to some opinions, this will not get you listed in spam engines -
it's a legitimate way for you to send emails.
A partial example for use with PHPMailer:
$mail->AddAddress("undisclosed-recipients:;");
$mail->AddBCC("email1@anydomain.com,email2@anyotherdomai n.com,email3@anyalternatedomain.com");
Many email service providers restrict the number of emails that can be sent
in any given time period. Often that is between 50 - 60 emails maximum
per hour or per send session.
If that's the case, then break up your Bcc lists into chunks that are one
less than your limit, and put a pause in your script.