You're formatting messages the wrong way
By Iain Thomson in San Francisco 11 Oct 2017 Attention anyone using Microsoft Outlook to encrypt emails. Researchers at security outfit SEC Consult have found a bug in Redmond's software that causes encrypted messages to be sent out with their unencrypted versions attached.
You read that right: if you can intercept a network connection transferring an encrypted email, you can just read off the unencrypted copy stapled to it, if the programming blunder is triggered.
Full Article.