Troubleshooting

Coupon code is missing in the email

Please make sure that you are using correct variable in the transactional email template. 

{{var subscriber.coupon_code}}

Magento is not sending success email if subscription confirmation is enabled

Magento is not sending it by default, but it's easy to change.

1. You have to make a copy the file:

from: app\code\core\Mage\Newsletter\Model\Subscriber.php

to: app\code\local\Mage\Newsletter\Model\Subscriber.php

2. Open new file and replace this part of code:

public function confirm($code) {
    if($this->getCode()==$code) {
         $this->setStatus(self::STATUS_SUBSCRIBED)
             ->setIsStatusChanged(true)
             ->save();
         return true;
     }
     return false;
}

to this

public function confirm($code) {
    if($this->getCode()==$code) {
         $this->setStatus(self::STATUS_SUBSCRIBED)
             ->setIsStatusChanged(true)
             ->save();
         $this->sendConfirmationSuccessEmail();
         return true;
     }
     return false;
}

3. Clear the cache and test it.