All clients flag a NIP-05 in some visual way if it is invalid. This can happens for a misconfiguration but more frequently when someone try to impersonate. The problem is that this "flag" (e.g. green/red icon, open/closed lock) is not always obvious, also because it is often next to the profile picture, and newcomers may be confused and deceived. Moreover, an incorrect NIP-05 does not always correspond to spam/scam, so it cannot be further highlighted.

Best pratice proposal: just hide invalid NIP-05s in feeds and threads, and show them only in the profiles, with a proper description of the problem.

#nostrdesign