OneDrive should produce an error or warning message if it fails to (or chooses not to) send an invitation email
When sharing a folder with somebody on OneDrive for Windows Desktop, if OneDrive does not send the email to the intended recipient, it should warn the user.
Sometimes OneDrive tries to send an email but fails (you have to check in your Outlook outbox to see if the email was sent). If this happens, the user is not informed.
Sometimes OneDrive chooses not to send an email. For example, if OneDrive thinks the folder has already been shared with the recipient, it doesn't send the email because it thinks it has already been sent. This is not ideal. If an email fails the first time, the user may try again and again and is never told by OneDrive that the invitation email was not sent.
I suggest two new warning messages:
1) The folder has been shared but the invitation email was not sent due to an unhandled error. You should send this link to the recipient to ensure they can share your file or folder [sharing link]
2) An invitation email was not sent to the recipient because the folder had already been shared with them. If they haven't already received a link, you should send them this [sharing link]