Any emails that you reply to or forward will get trashed re:[EXTERNAL]fwd:[EXTERNAL] etc... Eventually people will disregard the flags because of the noise. It&#x27;s a very narrow circumstance where this would actually prevent fraud. You&#x27;re looking for someone who would normally wire $BIGDOLLAR without verifying it, yet also pay attention to warning flags which are almost always present.<p>You don&#x27;t win this battle by trying to block all the possible ways in. Instead you create one approved process for handling $BIGDOLLAR transactions.