I have a PowerPoint VSTO - I want to create a PDF of the selected slides and create an email. This worked good so fare with the Desktop Version of Outlook. Changing to the "New" Outlook, this doesn't provide such an API. The way I figured out at the moment is to create an .EML file and let it open by the default mail application - which is the "NEW" Outlook. But this has some disadvantages:

• Signature is not automatically added
• I have to create a temp .EML file and delete it later - I cannot just handover a memory stream to Outlook
• Sometimes I get an error "New Outlook" cannot process the mail - and then the mail is opened in the Desktop version - but sending it puts them in the outbox of the desktop and will only be sent when the desktop version is opened

I cannot setup in my tenant an App so I can add the tenant and App ID to my code to authorize a new created mail, because this must be dynamically for individual customers.

Who has a good and stable working solution which works either for desktop or "NEW" Outlook version? Goal is to create those emails out of a PowerPoint AddIn.

Thanks for any advice.