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Mail flow in Exchange Online

Exchange Online

Applies to: Exchange Online

Topic Last Modified: 2015-09-15

As an Office 365 customer, all mail sent to your organization passes through Exchange Online Protection (EOP) prior to reaching your mailboxes. This ensures that spam doesn’t reach your users. If you host all of your mailboxes in the cloud with Exchange Online, mail reaches your mailboxes after passing through EOP processing. In the same manner, if you sign up for EOP and continue to host your mailboxes on premises (called a standalone scenario), perhaps to continue taking advantage of your existing infrastructure, mail passes through EOP for processing and is routed on-premises for delivery. For outbound delivery, the process works in reverse.

There may be cases where you may want to customize your mail flow. You might do this because you want to set up hybrid mail flow, where you host some of your mailboxes on premises and some in the cloud, or to route mail to a specific location. The following sections provide more detail.

For more information about how your email is protected with EOP, see Exchange Online Protection overview.

For information about migrating your email to Exchange Online, see Ways to migrate multiple email accounts to Office 365.

Exchange Online includes connectors, which behave similarly to Receive connectors and Send connectors in Exchange Server on premises. You can use them to set up custom mail flow.

Configure mail flow using connectors in Office 365 introduces connectors. Scenarios include ensuring secure communication with a partner organization and setting up a smart host.

In a hybrid deployment you customize your mail flow to enable communication between your on-premises and cloud messaging environments. When you set up a hybrid deployment, connectors are created to direct mail flow. However, you don’t create them manually. Microsoft has created tools to automate the hybrid-setup process.

The Exchange Server 2013 documentation includes a section, Exchange Server 2013 Hybrid Deployments, that gives you the background information and steps to set up a hybrid deployment.

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