When copy and paste pre-existing recipients, Office.context.mailbox.item returns recipients without email addresses. This library is used in a outlook add-in, as the recipient email address is not returned, the add-in prompts an error.
When copy and paste pre-existing recipients, Office.context.mailbox.item returns valid recipient email addresses.
When copy and paste pre-existing recipients, Office.context.mailbox.item returns recipients without email addresses.

Repro steps:
Adding users to email compose

Cut “Cal Substrate Test 1” from Cc and paste to To field -> Warning shows up

There are approximately 700 api call failures due to this error.
Thanks for reporting this issue regarding recipients API. It has been put on our backlog. We unfortunately have no timelines to share at this point
Internal tracking id: Office: 4516844
We have fixed the bug and the fix should be available in build 16.0.13408 or later. When an updated build is available depends on the release channel a customer is on.
[Outlook Add-ins Engineering Team]
Great, thanks for the quick fix.