I think that it has nothing to do with email/spam filters. And if they are only emailing then how will they view top/weekly?
The OP wants an Activity Summary that includes activity (replies) for topics for which the user has already been notified by Watch First Post. Apparently those topics are suppressed.
Assuming that is correct then the following is a longer explanation:
- The OP is using
Watch First Postto reduce the number of emails sent to users. - The
Watch First Postnotifications generally suppress the Activity Summary. - But eventually no new topics are created frequently enough to suppress the Activity Summary.
- The Activity Summary doesn’t show any replies on topics they got first post notifications for.
- So the Activity Summary largely has no topics that those users are interested in.
So why not just suppress the Activity Summary if it is ineffective? The OP still wants it but needs this feature to make it useful for them.