Been using this plugin for the last two years and does some great things. I would like to suggest adding a separate email to be sent for confirming subscriptions vs unsubs. Right now a user of this plugin needs to create multi-purpose copy for two very different events from a user's perspective. From a code perspective they are the same so I see the thinking behind it.
However, many times I find people confused by the messaging. therefore having separate text blocks would be VERY VERY helpful. Such as this for Subscribing:
"Thanks for signing up. You are almost done - in an effort to protect your information & privacy we have sent you a confirmation email with contains a link to ensure it was you that actually signed up. Once you confirm your identity you will be receiving post notifications."
Having this relate exactly to the user's actions helps raise the conversion rate of "opt-ins" which is the point, right?
On the other side, for Unsubs:
"Sorry to see you go. Our unsubscribe process requires you to confirm your request by clicking the link we have sent you in a separate email. We apologize for the inconvenience but we do that to confirm your identity.
If you change your mind you can re-subscribe on the site or from the link below. "
Please consider adding this or tips on how to ourselves.