Ability to forward signed emails
Currently, we cannot forward emails that are signed ("createForward" endpoint in the Graph API). Instead, a cryptic error message ("The specified object was not found in the store., Cannot open attachment.") is returned with HTTP status code 404.
After discussion with the support, it appears to be a design decision to exclude signed emails from the built-in forward functions. As this is an unintuitive design decision that is also currently not documented, this can be a big show stopper in many projects (I assume that most people are not aware of this limitation of the Graph API).
It would be great if the design can be extended, so that signed emails can be forwarded as well in a similar manner to Outlook (i.e. strip the signature and keep everything else).