Authentication - SMTP Authentication on Exchange

This article contains information on configuring SMTP Authentication Exchange 2013 SMTP Connectors using Mimecast local accounts to ensure secure outbound email delivery when dynamic IP addressing is used.

Typically, Mimecast Support will configure Authorized Outbounds for each Mimecast Account during the Implementation Process. Authorized Outbounds control which IP addresses are allowed to send outbound emails to Mimecast and ensure that unknown mail servers cannot relay off Mimecast Services.

For customers using dynamic IP addressing for outbound emails, a fixed Authorized Outbounds cannot be configured. Mimecast, therefore, requires authentication from the sending mail server to ensure that the connection is validated.

This authentication is configured as part of the SMTP Connector created for outbound email delivery from the Exchange Server to Mimecast. For more information about configuring SMTP Connectors, see the following articles below:

• Setting up an SMTP Connector: Exchange 2016 / 2013

Before configuring the authentication for your SMTP Connector, a Mimecast local account is required. A new local account can be created, or an existing account can be used. For more information on creating a local account on Mimecast, see the full article:

• Creating / Editing Mimecast Users

Once the account has been created, the SMTP Connector needs to be amended to configure basic authentication using this account to provide the credentials.

Configuring SMTP Authentication on Exchange 2013 SMTP Connector

Before configuring the authentication for your SMTP Connector, a Mimecast local account is required. A new local account can be created, or an existing account can be used.

Once the account has been created, the SMTP Connector needs to be amended to configure basic authentication using this account to provide the credentials.

1. Open Exchange Admin Center (EAC).
2. Navigate to Mail Flow | Send Connectors.
3. Select the Connector in the list, and click the Edit icon
4. Add two Smart Hosts for your environment, using the Mimecast service addresses provided by our Connect team. For additional information on Smart Host routing, view the full article: https://docs.microsoft.com/en-us/exchange/mail-flow/connectors/outbound-smart-host-routing?view=exchserver-2019
5. For each Smart Host, select the Basic Authentication method and complete the user account details as configured earlier.
6. Click the Save button.

   To confirm that mail is flowing, send an outbound email to an external email address. Navigate to the Message Center | Accepted Messages menu item and refresh the screen until you can see the details of the email you have just sent.