We have o365 with a local domain synced. We do not have exchange on premise. I configured a SMTP relay server running under username "smtp_user" (for example). I then added "smtp_user" as a send as delegate for each one of our users.
This is working successfully. Recipients receive the email and it shows as coming from the sending user.
But the sending user does not have a copy of that email in their sent box. Is there a way to have emails sent from a relay server appear in a users sent box?