I recently upgraded from Magento CE 18.104.22.168 to 1.9.1.
I read that emails are supposed to be sent via a queue/cron but after some testing this turned out to not be true.
When I place an order the email is sent immediately, just like before upgrading to 1.9.1.
I put some Mage::log() statements in Mage_Core_Model_Email_Queue::send() to verify. The method is being executed via cron every minute, but no messages are ever present in the queue to be processed.
My question is this: Do I need to enable some setting somewhere or did I miss anything?