I have Outlook 2013 connecting to Exchange 2013 in Online Mode and not cached mode. Using ECP, I have a user full access rights and send as rights to a shared mailbox. The user can see,delete, and read emails in the shared mailbox. When the user tries to send mail as the shared mailbox, the email is getting stuck in the user's outbox folder and never sends. Not even after manually clicking on send and receive. I also do not have the registry key DelegateSentItemsStyle
Any idea how I can fix this?