E-mail coexistence is supported between local Microsoft Exchange Server environments and Microsoft Exchange Online. The first step in establishing e-mail coexistence is to add to Microsoft Online Services the domain that you are currently using to send and receive e-mail. For more information, see About Using Your Domain with Microsoft Online Services.

During e-mail coexistence, you will have users with local Exchange Server mailboxes and users with Exchange Online mailboxes. E-mail sent between your local Exchange Server environment and Exchange Online will be exposed to the Internet. We recommend installing Transport Layer Security (TLS) in your local Exchange Server environment to secure e-mail traffic between your environment and Exchange Online. For information about installing TLS, see Secure Your E-Mail Traffic.

See the topics in E-mail Migration Help for a basic understanding of moving mailbox content to Microsoft Exchange Online. For more in-depth information, see the Microsoft Online Services Deployment Central site.

For the latest information, tips, and tricks for the migration and coexistence features of Microsoft Online Services, visit theMicrosoft Online Services Migration and Coexistence support pages.

Required Permissions

• You must have Administrator permissions in your Microsoft Online Services organization to implement e-mail coexistence.
• You must have Exchange Administrator permissions to implement TLS in your Exchange Server environment.
• To install directory synchronization, you must have local Administrator permissions on the computer, Enterprise Admin permissions in your local Active Directory service, and Administrator permissions on Microsoft Online Services.