I’ve got a domain that uses Google Apps to handle all mail activity.
I would like to use MiaB to ONLY send mail from 1 account on that domain, while the receiving and sending of all other accounts is still done through Google Apps.
For this, I think I need to set custom MX and SPF records.
Currently, the domain is set with only Google MX records: ASPMX.L.GOOGLE.COM, an SPF record that (also) includes my current smtp host and a google verification key as TXT.
You will not need custom MX records unless you plan to deliver email for a subdomain or reroute all mail to Mail-in-a-Box. You will however need to include the MIAB in your SPF records and add the DKIM key to the domain zone. Note that the instructions below are from a Google Apps for Education deployment, and if you’re using a free Google Apps account some options may not be available.
In order to deliver email for a specific account to the MIAB you’ll need to create the account in Google Apps as a normal user. Then head to Admin -> Apps -> Google Apps -> Gmail -> Advanced Settings.
Under Email Routing look for Receiving Routing and create a new policy using the settings you need. Make sure the Email Messages to Affect options for Inbound and Internal - receiving are both selected.