office 365 Mail flow in Hybrid Deployment

1. Scenario 1 – MX record points to Office 365, and Office 365 filters all messages
2. Scenario 2 - MX record points to Office 365, and mail is filtered on-premises
3. Scenario 3 – MX record points to your on-premises servers
4.  Scenario 4 – MX record points to your on-premises server, Your on-premises server relay messages to the internet through Office 365.

 

Scenario 1 – MX record points to Office 365, and Office 365 filters all messages

• I’m migrating my mailboxes to Office 365, and I want to keep some mailboxes on my organization’s mail server (on-premises server). I want to use Office 365 as my spam filtering solution and would like to send my messages from my on-premises server to the internet via Office 365. Office 365 sends and receives all messages.

Most customers who need a hybrid mail flow setup should allow Office 365 to perform all their filtering and routing. We recommend pointing your MX record to Office 365 because this provides for the most accurate spam filtering. For this scenario, your organization’s mail flow setup looks like the following diagram.

 

Scenario 2 - MX record points to Office 365, and mail is filtered on-premises

• I’m migrating my mailboxes to Office 365, and I want to keep some mailboxes on my organization’s mail server (on-premises server). I want to use the filtering and compliance solutions that are already in my on-premises environment. And all messages coming from the internet to my cloud mailboxes or messages sent to the internet from my cloud mailboxes need to route through my on-premises servers.

If you have business or regulatory reasons for filtering mail in your on-premises environment, we recommend pointing your domain’s MX record to Office 365 and enabling centralized mail transport. This setup provides optimal spam filtering and protects your organization’s IP addresses. For this scenario, your organization’s mail flow setup looks like the following diagram.

 

Scenario 3 – MX record points to your on-premises servers

• I’m migrating my mailboxes to Office 365, and I want to keep some mailboxes on my organization’s mail server (on-premises server). I want to use the filtering and compliance solutions that are already in my on-premises email environment. All messages coming from the internet to my cloud mailboxes or messages sent to the internet from cloud mailboxes must route through my on-premises servers. And I need to point my domain’s MX record to my on-premises server.

As an alternative to Scenario 2, you can point your domain’s MX record to your organization’s mail server rather than to Office 365. Some organizations have a business or regulatory need for this setup, but filtering typically works better if you use Scenario 2. For this scenario, your organization’s mail flow setup looks like the following diagram.

 Scenario 4 – MX record points to your on-premises server, which filters and provides compliance solutions for your messages. Your on-premises server needs to relay messages to the internet through Office 365.

• I’m migrating my mailboxes to Office 365, and I want to keep some mailboxes on my organization’s mail server (on-premises server). I want to use the filtering and compliance solutions that are already in my on-premises email environment. All messages sent from my on-premises servers must relay through Office 365 to the internet. And I need to point my domain’s MX record to my on-premises server.

For this scenario, your organization’s mail flow setup looks like the following diagram.

Ref: https://technet.microsoft.com/en-us/library/jj937232(v=exchg.150).aspx