Log unknown key prefixes

dovecot/keyproxy.go

@@ -90,6 +90,7 @@ func (s *KeyLookupProxy) Lookup(ctx context.Context, key string) (interface{}, b
 	case strings.HasPrefix(key, "userdb/"):
 		return s.lookupUserdb(ctx, key[7:])
 	default:
+		log.Printf("unknown key %s", key)
 		return nil, false
 	}
 }