By default, the Google Apps mail servers deliver each incoming email message to the inbox of the recipient. If the message is addressed to an unknown recipient — that is, to a user who does not exist in your domain — the mail server discards the message.
The email routing options enable you to change this default behavior in two ways. You can instruct the mail server to:
- Deliver mail for unknown recipients to a catch-all address rather than bouncing the messages
- Forward mail to an additional mail server or email address
When to use email routing
You designate an existing user account as a catch-all address to receive messages that are addressed to non-existent users in your domain. It captures mail for previously deleted users or when the sender has misspelled the user's name (the part to the left of @).
There are a few situations when you want to forward mail to additional mail server or address:
- To set up split delivery, where some users in your domain have a Gmail inbox and others use a legacy system inbox. The Google Apps mail servers pass messages for non-Gmail users on to your legacy email system. (Learn more about configuring split delivery.)
- To set up dual delivery through the Google Apps mail servers. With dual delivery, the Google Apps mail servers forward copies of all incoming mail to the secondary server for delivery to a second inbox for each user. (Learn more about dual delivery.)
- To add a secondary server to serve as a backup that archives the mail for your domain.
- To use a secondary server (instead of a catch-all address) to handle messages addressed to unknown recipients.
- To forward messages for particular users to their secondary email address.
For all but the last option, you configure email routing rules for your entire domain. For the last option, you configure an email routing rule for each of the affected users.
Note that you cannot forward mail to another Gmail or Google Apps account using domain-level email routing.