I use civimail on a drupal 7/CiviCRM 4.7.8 and have done so for many years.
Recently civimail has started sending out an email multiple times to the same email address even though
1) the email address only exists once in the system.
2) In the sql database under civicrm_mailing_recipients it only says the email contact receives it once and this is borne out in the activities tab.
This is not just happening with one email address - it's happening with hundreds of email addresses.
Any ideas on where to start troubleshooting?