Unsubscribe feature for non registered users
Based on MUTE feature, implement Unsubscribe for non registered users.
When sending the mail notification:
- if user exists, then current link to manage subscription,
- if user does not exist just provide instead a link 'click here to unsubscribe' with email address in an encrypted blob as query string, which goes to the special mute management page for non authenticated users, and adds a global mute for this email in the DB.
Then if one day a user with that email address logs in for the first time this DB mute entry is assigned to this new user, and management / delete of mute can then be done.
Possible alternative, if you don't want to mount the mute to an email but instead to a user id for consistency we can make something similar to whats done in add member to channel. Would need the username field to be nullable in User table.