Mail flow in Exchange Online
Applies to: Exchange Online
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 Mailbox Migration to Exchange Online.
Exchange Online includes Inbound connectors and Outbound 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. For example, you may want mail sent from your organization to a specific domain to pass through a smart host. You can configure that scenario with an Outbound connector.
For more information about using Inbound connectors and Outbound connectors to set up a custom mail-flow scenario, see Configure custom mail flow by using connectors in the EOP documentation. Additionally, New-InboundConnector and New-OutboundConnector show you how to create connectors using PowerShell.
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, Inbound connectors and Outbound 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.
The following are additional topics related to mail flow in Exchange Online: