* stable-3.0: OutgoingEmail: Sanity check recipients of multipart and plaintext OutgoingEmail: Log when email is sent as multipart and plaintext OutgoingEmail: Log the reason that email is not being sent OutgoingEmail#send: Check first if email sending is enabled Upgrade jackson-core to 2.10.0 Change-Id: I51a03d657f0631b1913be10ff8cb7dafca42232b