Email, unless you encrypt it yourself, is not encrypted at rest. This means any mail server or relay which your email lands on can be openly mined and analyzed

Email, unless you encrypt it yourself, is not encrypted at rest. This means any mail server or relay which your email lands on can be openly mined and analyzed transparently, and without any evidence (which is how GMail works, BTW). If you're sending sensitive financial information over the mail, it can be read, classified, tied to you and be used against you if required. So, we have a directive to not email anything financial to the recipient by default.