ConvertKit places a premium on improving the deliverability for its content creator base. A subscriber is someone who has manually confirmed their email. Some email subscribers may also be automatically confirmed after they’ve put their information on your forms. Any subscriber who hasn’t opened or read anything on their email account in the past 90 days will be defined as “cold,” and if the system can’t reach a subscriber, they will be defined as “bounced.” If a subscriber doesn’t respond to the confirmation emails you send, they will be defined as “unconfirmed.”