If you are using an Amazon account for your optin email and are having email deliverability issues, it may be due to the classification of your email with Amazon.

If you account is newly created with Amazon, it may still be “Sandbox” mode. While under this classification you will not be able to mail to people outside of your verified email list in amazon. 

To remove the restriction on recipient addresses and increase your sending limits, you need to open a case in Support Center by using the following instructions: http://docs.aws.amazon.com/ses/latest/DeveloperGuide/request-production-access.html

Once you have full sending access all of your Amazon emails should send without issue.