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Scenario: Outbound smart hosting


Applies to: Exchange Online, Exchange Online Protection

Topic Last Modified: 2015-03-30

A smart host (also known as a relay host) is a server that redirects outbound mail. You can configure a connector to redirect outbound mail from your Exchange Online mailboxes through one of your on-premises servers, which can apply rules or perform additional processing on each message.

With Office 365, you get product updates as they become available. A new experience for connectors is rolling out right now and there is information to help you with the current experience, and the new one. First, check which version of connectors your business has.

To find out which version of connectors your business has, click Admin, then click Exchange to go to the Exchange Admin Center. Next, click mail flow, and click connectors. If any connectors already exist for your organization, they are listed here. If you have the current version of connectors, the screen has two sections, one for Inbound connectors, and one for Outbound connectors. If you’re using this version, you have found the right information. However, if you have the new version of connectors, there’s just one section on the screen, and connectors are set up using a wizard-like experience when you click the plus symbol +. If you’re using the new version of connectors, there's some new content available; start with the topic Configure mail flow using connectors in Office 365 instead.

More content for Inbound and Outbound connectors:

Both versions of connectors work the same way in the background, so you don’t need to change any settings when the experience changes.

This scenario is appropriate when you have an on-premises protection appliance or other compliance solution that you want to process outbound mail.

In this example, Contoso has a server that processes outbound mail. Messages are directed to the on-premises server, prior to delivery.

The following video shows the configuration steps:

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Contoso’s mail flow is illustrated in the following graphic:


In order to configure this scenario, you must create an Outbound connector that routes mail to your specified server. Follow these steps to configure the connector:

  1. In the EAC, navigate to Mail Flow > Connectors. Under Outbound Connectors, click Add Icon to create a new connector.

  2. Give the connector a name. For Connector Type, choose On-premises for this scenario. Add a description in the Comment text box. For the security connectivity requirements, you can select Opportunistic TLS (a TLS connection is attempted, but it rolls over to an SMTP connection if the receiving email server is not configured to use TLS) or one of several TLS certificate options:

    • Self-signed certificate Created within your organization, this certificate is used to encrypt the channel.

    • Trusted certification authority (CA) Validates that the recipient certificate is issued by an authorized certificate authority, that it isn’t expired, and that it is authentic.

    • Recipient certificate matches domain Validates that the certificate domain matches what you enter.

  3. In the Outbound Delivery section, choose Route mail through the following smart host, and then enter the fully qualified domain name or IP address of the destination server. This selection sends messages to the smart-host destination, regardless of the recipient’s MX-record destination.

  4. Choose Route all accepted domains through this connector to apply this connector to all of your provisioned domains.

    In the add domain dialog, you can specify a specific domain you want to apply the connector to, such as contoso.com. If you add a domain, it appears in the Domains list.
  5. Click save to save the connector. It appears in the list of connectors. If you have difficulty saving the connector, check to make sure you completed all of the required fields. Make sure ENABLED is checked. Later, you can edit the connector’s settings by clicking Edit icon.

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