The first rule of any subscription - user must manually turn on subscription. All others methods is a spam.

Sorry to resurrect the dead. That first rule is good, it applies to many places. But the OP might had had a valid reason, like I do. I am running PunBB on my Intranet, I created the user list, and to encourage (or rather, insist) on participation, this setting is wanted. I am not spamming per se, this is a work installation, to discuss work related things. It is mandatory.

In the pun_users table I changed the default for 'auto_notify' default value to '1'.

I've tested and users can still change their setting as they want, it just starts as checked.

I'll see if I can code it myself, as my user base is asking for it.

Right now, the default is 'not subscribed by default' for each user.  People can change it for themselves to "subscribe by default", or they can change it on a post-by-post basis.

I would just like the initial, default, per-user setting to be "subscribe by default".  Obviously if they don't want that setting, they can change it.

But if you need this - you need write small extensions that turn this settings on for every new users.

Now it appears everyone needs to manually subscribe to a thread.

Is there a way to change this behavior so that users are subscribed to a topic by default?