Check the version of your licence
Since Letter Opener 10, we decided to switch our payment model to subscription to get rid of biases towards users who purchased in between major upgrades. If you have a license key for any Letter Opener Version below version 10, you will have to sign up for a new one-year subscription to upgrade your licence.
If you purchased a previous version of Letter Opener for macOS Mail after September 26, 2016, we will credit your new subscription with all days short of a year since your previous purchase. To check if you get free days added to your new subscription, click here.