It isn't needed, at least for the metadata part. see "Mail Covers": http://www.nytimes.com/2013/07/04/us/monitoring-of-snail-mail.html?pagewanted=all&_r=0 http:

It isn't needed, at least for the metadata part. see "Mail Covers": http://www.nytimes.com/2013/07/04/us/monitoring-of-snail-mail.html?pagewanted=all&_r=0 http://www.nytimes.com/2013/07/04/us/monitoring-of-snail-mai...