Connect Application: Creating an Outbound Email Flow Connector

Document created by user.oxriBaJeN4 Employee on Apr 14, 2016Last modified by user.oxriBaJeN4 Employee on Oct 18, 2018
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Applies To


This page applies to new clients connecting with Mimecast using the Connect Application. If you are not using the Connect Application, click here.




In order to send emails from your mail server through the Mimecast gateway, you are required to create an SMTP send connector with our smart hosts.

Your smart hosts are displayed in the Connect Application. Using a single connector with two smart host ensures there is round-robin traffic, and provides contingency in the unlikely event of a failover.


The process of creating an outbound mail flow connector differs according to the Exchange version you are using:


Office 365

Mimecast has observed that this process can only be successfully completed using Internet Explorer. This is due to an issue with the controls used in the final validation step.

To create an outbound email flow connector in Office 365:

  1. Log in to the Office 365 Administration Console.
  2. Select the Admin | Exchange menu item. The Exchange Admin Center is displayed.
  3. Select the Mail Flow | Connectors menu item and create a new Connector.
  4. Complete the New Connector - Select Your Mail Flow Scenario dialog as follows:

    FromSelect "Office 365" from the drop down list.
    ToSelect "Partner Organization" from the drop down list.
  5. Click the Next button.
  6. Complete the New Connector - New Connector dialog as follows:

    NameEnter a name for the Connector.
    DescriptionOptionally, enter a description for the Connector.
    Turn It OnSelect this option to enable the Connector.
  7. Click the Next button.
  8. Select the Only When Email Messages are Sent to These Domains option.
  9. Click the ico_plus.png icon to add the recipient domains that should use this connector.

  10. Enter a value of * to route all outbound emails through Mimecast.
  11. Click the OK button.
  12. Click the Next button.
  13. Select the Route Email Through These Smart Hosts option.
  14. Click the ico_plus.png icon to add the smart hosts from the table below for the region where your Mimecast service is hosted.
    RegionOffice 365 Account Hostnames
    Europe (excluding Germany)


    North America

    South Africa



  15. Click the Save button.
  16. Click the Next button.
  17. Select the following options:
    • Always use Transport Layer Security (TLS) to Secure the Connection (recommended)
    • Issued by a trusted certificate authority (CA)
  18. Click the Next button to verify your settings.
  19. Click the Next button.
  20. Add an email address of a recipient from a domain external to your organization.
  21. Click the Validate button.
  22. Once Office 365 has successfully validated your settings, click the Save button.


On Premise / Hybrid


For more information on how to create an outbound mail flow connector, view the relevant article below:


If you utilize non-static public IP addresses, refer to the Configure SMTP Authentication on Exchange page.


Hosted Exchange


To set up your outbound email, forward our outbound routing instructions to your HEX provider to make the required changes. Ensure they consider the following when setting up your outbound email:

  • In a multi-tenanted HEX environment, there are normally a number of customers on one server sending email outbound via a single Exchange send connector. If one of the customers on the HEX platform implements Mimecast, their outbound email must be separated from the rest of the clients on that HEX platform.
  • All outbound email should then be sent to Mimecast for delivery, as opposed to being sent to the internet using the standard Exchange send connector. This is called Sender Address Based Routing, which is not a standard Exchange function.
  • To implement Sender Address Based Routing, either a third party tool or additional hardware is required to send outbound email directly to Mimecast.
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