Hello O365 Community,
We receive a great deal of feedback on our current SMTP relay documentation. Because of this, and because of the advanced features that we introduced in the latest version of Exchange Online, we're working on revamping our documentation to cover all of the relay scenarios.
The Wiki is a good look at how the scenarios are broken down, but we will be expanding our explanations. For now, here's a summary of what we're looking at:
Direct Send: In this scenario, you don't need to use Office 365 at all. This is for robust applications or devices that can resolve MX addresses on their own, and send mail directly to their destinations.
Exchange Online Relay: In this scenario, the application or device relays mail through the Exchange Online Datacenter using the smtp.office365.com address. This method requires authentication, which can be broken down into the following types:
- You want the application or device to use one specific set of credentials; e.g. printer@contoso.com. For this scenario, you will create a shared mailbox, and use that mailbox credentials to authenticate.
- You want the application or device to be able to use a non-specific user's credentials; i.e. anyone with an O365 EXO license can walk up and use their credentials to send mail.
Exchange Online Protection Relay: In this scenario, you are using EOP inbound connectors to accept mail from your on-premises organization or smart host, and then EOP relays it on. This method also requires authentication, but instead of using user credentials to authenticate, you must authenticate by certificate or by IP. The methods we'll be documenting include the following:
- Exchange Online only: You will be configuring the inbound connector to accept mail by IP or certificate. This is the most common scenario.
- EOP Stand-Alone environment: This is the normal configuration for folks who are using EOP in a standalone configuration with an on-premises environment.
- Exchange Online Hybrid: similar to the above, you configure your on-premises mail flow through normal setup using the Hybrid Configuration Wizard.
If you have any questions or comments regarding SMTP routing, or have suggestions on scenarios, don't hesitate to add them to this thread.