Hi @pina,
When you undergo major changes to your email types, it’s a great practice to notify your subscribers and let them update their email preferences. Here’s a walkthrough of how to set up a link that will pull up the subscription settings. (Please note: the HuBL token is called {{unsubscribe_link}} , but don’t concern yourself with the term “unsubscribe” . This token will simply direct the user to their specific email preferences page.)
The second part of your question, to interact with those who have unsubscribed, can be corrected in two different ways. First, you could send the activation emails that you mentioned as a transactional email. Read more about transactional emails here.
If transactional emails aren’t a possibility, you could set up resubscription emails for contacts who have unsubscribed, and when they sign up for your trial, are able to resubscribe to emails (and receive the activation email). See how resubscription emails work.