Android has a way to filter out spam messages and they're hidden from the main messages list. However KDE Connect SMS App on the PC doesn't filter these out. SMS spam is on the rise at least here in Australia and it would be nice if KDE Connect filtered them out.
To be very picky, this is not true (to my knowledge) (In reply to Justin Zobel from comment #0) > Android has a way to filter out spam messages ... Google Messages (and presumably other apps) have a way of filtering out spam messages. As far as I can tell, this is 100% handled at the application layer, so there is no way we can get the information by calling system APIs. If someone knows otherwise, please share the doc links, etc. Marking this bug as confirmed, since it is true that KDE Connect does not filter spam messages and ideally should.
Spam messages don't show in the main SMS window on the phone, therefore they are being filtered or at least not included in the main messages list that a user would access. KDE Connect does show them, therefore I assumed (perhaps incorrectly) that all SMS are together and that they are filtered by the SMS app on Android.