Imagine an unknown user mailing to a category that has restricted access. One of the known users reply there, so the unknown user gets a notification by mail.
In that mail there is the line that says Visit Topic or reply to this email to respond. But when visiting that topic, two things can happen:
- the forum is closed and the new user needs to login anyway
- the forum is not closed, but the user has no access to the category, because he’s not in that group
For point 1, the new user should get some assistance to create a password. It’s totally not clear what to to there.
For point 2, maybe the user shouldn’t have the option to visit the topic at all.
Simplest solution: have staged users get custom copy in their mail notifications. No visit this topic, just reply by mail.