Office.js - Let our Office MessageComposeCommandSurface Add-ins read *all* the users email info

Trying to write a useful add-in for Outlook is excessively limited, owing to a large number of important bits of user context not being accessible to us.

When a user installs our Add-in they're wanting to use new features that we build for them, applied into the current email they are composing.  This means that our Add-in should be able to read everything about that email they are composing, so it can do its job properly:

It would be useful if the following could be included added:-

getAttachmentContentAsync for *all* the users attachments (not just appointments/etc)

Settings: Importance and Sensitivity
Voting and Tracking Options: Delivery-receipts and read receipts
Security: Encryption, digital signing, and labels
Delivery options: reply-to email address, send-delay and expires-after info
and Categories

See https://github.com/OfficeDev/office-js/issues/2111

and https://github.com/OfficeDev/office-js/issues/2113