I just upgraded to Magento CE 1.9.1 from 1.6.2 and we're having issues with the sales order emails now.
In system > config >sales order emails > order > send order email copy to, we have two emails set.
Magento sends an order confirmation email to the customer, and two to each of the emails we have in the send order email copy box. If we put three emails, magento sends three emails to those addresses.
This appears to be the same issue in this thread. Magento after upgrading order update email sending duplicate emails
Does anybody have any idea what the issue could be?