How to setup Gsuite SMTP relay on Office 365?

New Contributor


Please tell me how to setup G-Suite SMTP relay ( ) on Office 365? This is to relay outgoing emails from Office 365 through G-Suite. We are migrating from Office 365 to GSuite. The MX records are now pointing to Google.

5 Replies

You might want to try explaining what exactly you are trying to achieve here, with details.

I have 2 domains with mail accounts hosted in Office 365. I am going to migrate this to G-suite. The MX is now pointing to G-Suite and I have setup dual-delivery on G-suite and the incoming mails are getting in both mailboxes. Now I wanted to make sure that the outgoing mails from Office 365 mailboxes are routed back through the G-Suite. So the mails that are sent from O365 mail accounts will be available on the sent items of the respective Gmail accounts. I want to set this to avoid the delta migration.

Same scenario, I was wondering if setting to Internal Relay, instead of Authoritative and also setting up a connector to route to G-Suite is the solution? rejected your message to the following email addresses:

Your message wasn't delivered because the recipient's email provider rejected it. gave this error:
Mail relay denied [2a01:111:f400:7e14::201]. Invalid credentials for relay for one of the domains in: (as obtained from HELO and MAIL FROM). Email is being sent from a domain or IP address which isn't registered in your G Suite account. Please login to your G Suite account and verify that your sending device IP address has been registered within the G Suite SMTP Relay Settings. For more information, please visit p6-v6sm1401705itf.7 - gsmtp

If I need to whitelist something on the Google side. Please let me what to whitelist?

Hi @vishnu vishnu 


I have the same setup and problem as yours.  Have you already resolved the issue?