digests can be daily or weekly – you set that as admin…
a single email about subscription and the user going back to the topic could be quite problematic… that could be fair amount of data to be stored and needed to be accessed on posts… could really affect performance… and then its not really a subscription either…
I am not sure I want to go the route of unsubscribe links in the email… you wouldnt believe the amount of confusion users have when they get an email saying they have a new private message and when they click on the link, they get an accessed denied message… of course, its because they are not logged into the forum and thus cannot see the pm… would be same issue with unsubscribing… only worse, because at least with pms we have our own page template and can make things look better… for the unsubscribe they would get a really ugly mess and its not worth it to create a special page template just for a unsubcribe attempt when they are not logged in… plus its quite simple to unsubcribe from all topics/forums either via the popup or the profile… will think on it, but I dont think its in the future…