It's been a while but I was wondering if you would provide more details/clariifications.
1. Are you referring to the Export mail (exchange connector) action? If so, I seem to be getting Forbidden when attempting to use that action, despite being a member of the group that owns the mailbox, did you have to make any permissions changes to group/exchange to get that to work?
2. What is the mail ID that you're using when fetching the mail? ConversationID, ThreadID, PostID?