Outlook Javascript API to get control to addin on Saving as Draft or before sync to exchange server

We are working on an Outlook addin to make sure confidential information is not leaked using mail. Using the on-send feature using ItemSend, we were able to get the email fields and block the sendmail, if required https://github.com/OfficeDev/Outlook-Add-in-On-Send/tree/master/outlook-add-in-on-send

But there is an use case

1. User composes the mail and saves it to draft (without clicking on Send)
2. In outlook on web, composing a mail saves to draft automatically.

   How can the add-in get a callback when draft is synced to Outlook server so that add-in can decide whether it contains any confidential info ?

    

   Even though the mail is not sent to users,
   We have few scenarios where some platforms are not supported/dont have control over (like Outlook Mobile). So even if the confidential information is synced to the server, it can later be used to egress from the Outlook mobile.