An outbound mail gateway is a server through which all mail sent from your domain passes. The gateway typically processes the mail in some way — such as archiving it or filtering out spam — before delivering the mail. The Postini servers are an example of an outbound mail gateway: they filter (and possibly archive) outgoing mail before delivering it.
When you use an outbound mail gateway, the Google Apps mail servers pass all outgoing mail from your domain to the gateway server. You configure the gateway server to accept a stream of mail from the Google Apps mail servers. You may also need to update your DKIM configuration or the Sender Policy Framework (SPF) record for your domain.
To Configure an Outbound Gateway
- Sign in to the Google Admin console.
- From the dashboard, go to Apps > Google Apps > Gmail > Advanced settings.
- In the Organizations section, highlight the top-level org.
- Scroll down to the Outbound gateway section.
- In the Outbound gateway text box, enter the IP address of the outbound mail gateway server.
- Save your changes.
- Configure the outbound gateway server to accept and forward email from the Google Apps mail servers.
The configuration steps differ depending on the gateway server. For information about the IP addresses of the Google Apps mail servers, see Google IP address ranges.
If you authenticate outgoing email using an SPF record or DKIM, you may also need to update your configuration.