Hi,
I have an Office 365 shared mailbox setup to receive support calls. When an email is received I have workflow configured to create a case.I have "other actions" set to create a queue item for the case and to send an internal email notifying us of case creation.
I have also checked the "autoresponse email" using the Case Auto Response tenplate.
Everything appears to work fine, except that the emails are almost never sent.
In the System Job viewer I see this result for a new case coming in:

Clicking the email properties shows "This message has not yet been submitted"

I imagine the problem is that we're tying to "send as" the shared mailbox. The Test and Enable activity on the mailbox completes successfully, and every now and then an email does get sent correctly. But most of the time I just see errors authenticating. If I specify credentials in the mailbox it pops a message telling me they are not required.
Is this the wrong way of doing this using a shared mailbox? Should I be using a mailbox account instead?
Many thanks
John