OS X Server: Sending email invitations, notifications and alerts when an SMTP relay is required

OS X Server can send email invitations, notifications or alerts on behalf of many OS X Server services. These include Caching, Certificate, Disk, Firewall, Mail, Network Configuration, Profile Manager, Software Updates and Time Machine.

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When an ISP requires that an SMTP relay be used for outgoing mail, OS X Server can be configured to use the SMTP relay server provided by your ISP. 

OS X Server includes two built-in SMTP servers: OS X Mail Service and Sendmail. When OS X Server Mail service is configured and enabled, it's used to send out email invitations, notification or alerts. If the OS X Server Mail service is not enabled, Sendmail is used instead. 

If you use an SMTP relay, you should add your SMTP server address and authentication credentials (when required) to your OS X Mail Server configuration. Both the OS X Server Mail Service and Sendmail use the same configuration files and settings:

  1. Open Server.app
  2. In the Mail pane, select “Relay outgoing mail through ISP.”
    If this option is already selected, click the Edit button. A prompt appears where you can enter your relay server connection details.
  3. Click the box next to "Relay outgoing mail through ISP."
  4. Click the Edit button.
  5. Enter the relay server DNS name or IP address.

    If you need a custom port, you can specify a port number. Add a colon, followed by the port number, after the IP address or host name. For example, you could enter or example.com:587. You can disable your mail exchange (MX) lookups by entering your IP address or host name in brackets. For example, [] or [example.com].
  6. If you relay requires authentication before sending email, select “Enable SMTP relay authentication,” then enter the related user name and password. If you enable this option, your credentials are sent using the strongest authentication method available: CRAM-MD5, Digest-MD5, or Kerberos.

It is not necessary to start or restart the OS X Mail service. The settings you enter are automatically applied to both the OS X Server Mail Service and Sendmail.

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