Fixed client blocking mail deletion

Fixes #3144

Thanks to @kraaijmakers

src/map/clif.cpp

@@ -15249,10 +15249,12 @@ void clif_Mail_refreshinbox(struct map_session_data *sd,enum mail_inbox_type typ
 			}
 		}
 
+#if PACKETVER >= 20170419
 		// If it came from an npc?
 		if( !msg->send_id ){
 			mailType |= MAIL_TYPE_NPC;
 		}
+#endif
 
 		WFIFOB(fd, offset + 9) = mailType;
 		safestrncpy(WFIFOCP(fd, offset + 10), msg->send_name, NAME_LENGTH);