I have an intranet-type site where we host company training. One of the features we have is that when new safety protocols are put into place, we upload the new document and send an email to all employees to read the document, log in and certify that they read it.
This email can go out to 2500 employees in a single go. I used to send it by looping through the users and using wp_mail, but that was timing out as the numbers grew. So I started sending it using Blind Carbon Copy or Bcc headers. We need to switch to Mandrill so that we can feel more confident in the emails getting received, but what is the best way to send massive emails periodically to employees?
Any ideas would be great. The plugin is custom, so if we need to replace wp_mail, that would be fine...