Originally posted by @jasonjoh in https://github.com/microsoftgraph/microsoft-graph-docs/issues/2716
Regarding answer given by https://github.com/microsoftgraph/microsoft-graph-docs/issues/2716#issuecomment-580751583 No, internet headers just do not exist on the copy in Sent Items.
For shared mailbox messages in the sent items folder, we recently noticed using the graph api endpoint "https://graph.microsoft.com/v1.0/me/mailFolders/sentitems/messages?$select=internetMessageHeaders" we can access the headers. This was not the case earlier, so can we get a confirmation that this new feature can be relied upon.