Currently Microsoft Flow cannot handle digitally signed email (eg. to extract content or attachments like PDF)
The trigger "when a new email arrives in a Shared mailbox" won't fire if you select Has Attachment = YES (I suppose "when a new email arrives in mailbox" will not fire in the same case).
The encoding of digitally signed emails is different (MIME, S/MIME) and the connector actually does not properly decode that.
So the content is unreadable to the Flow.
The product team confirmed this and will update the documentation to reveal the limitation.
Actually, there is no plan from the team to support that kind of emails.
Please vote for that "feature" to be added.
on:
Trigger: when an email is replied to
Jesor
on:
Power BI Refresh Connectors JSON body