- You have a Microsoft Exchange Server 2013 hybrid environment.
- You install Cumulative Update 6 on the on-premises Exchange Server 2013 server.
- You enable centralized mail transport in the hybrid deployment.
Note Centralized mail transport routes outgoing email messages from the Exchange Online mailboxes through your on-premises Exchange servers. For more information, see Transport routing in Exchange 2013 hybrid deployments.
- A user whose mailbox is located in Office 365 sends an email message to an external recipient.