Welcome to managing mail flow with mailboxes in Exchange Online and On-Prem exchange. Over the next few minutes, we're going to review some of the ways that you can manage mail flow in an exchange hybrid environment. More specifically, we'll take a look at a complex mail flow scenario where the MX record points to Microsoft 365, and Microsoft 365 filters all emails. We'll also take a look at a scenario where the MX record points to Microsoft 365 and mail is filtered on-prem. And then we'll take a look at another scenario where the MX record points to on-prem servers. And then lastly, we'll take a look at the most complex scenario where the MX record points to the on-prem server which then provides filtering and compliant solutions for emails. 

In this last scenario, the on-prem server also needs to relay emails to the Internet through Microsoft 365. So, let's start with the first scenario I mentioned where your MX record points to Microsoft 365, which filters all emails. This scenario will often come up when an organization needs to migrate mailboxes to Exchange Online while keeping some mailboxes on-prem. In this type of setup, the organization wants to use Microsoft 365 for spam filtering and also wants to send messages from the on-prem server to the Internet via Microsoft 365. In this mail flow scenario, Microsoft 365 sends and receives all emails. Now this scenario is common because Microsoft recommends that most organizations that need a hybrid mail flow setup, allow Microsoft 365 to perform all mail filtering and routing. That being the case, Microsoft recommends pointing the MX record to Microsoft 365 in order to get the most accurate spam filtering. 

The image on your screen highlights what this mail flow setup looks like. Now the next scenario I want to take a look at is where you point your MX record to Microsoft 365 but you do your mail filtering on-prem. This type of mail flow scenario crops up when an organization wants to migrate mailboxes to Exchange Online, wants to keep some mailboxes on-prem, and wants to use an existing on-prem filtering and compliant solution that's already in place. In this scenario, all emails from the Internet to the cloud-hosted mailboxes and all messages sent to the Internet from those cloud-hosted mailboxes will route through the on-prem server. Organizations will sometimes use this mail flow configuration if they have some business or regulatory requirement for filtering mail in the on-prem environment. In these cases, Microsoft recommends pointing the email domains MX record to Microsoft 365 and enabling centralized mail transport. 

What this does is provide optimal spam filtering and it protects the organization's public IP addresses. The diagram on your screen shows what this type of mail flow setup looks like. Now, in this next scenario, you have a situation where you need to point your MX record at the on-prem server. You'll find it necessary to do this, for example, when you're migrating your on-prem mailboxes to Exchange Online but want to keep some of them on-prem while also needing or wanting to use a pre-existing on-prem filtering and compliance solution. In this type of mail flow configuration, all emails inbound from the Internet to the cloud mailboxes will route through the on-prem server. The same goes for emails sent to the Internet from the cloud mailboxes. For this reason, the email domains MX record needs to point to the on-prem server. The image on your screen shows what this type of mail flow architecture looks like. And now to wrap up this lesson, I do want to touch on this last scenario. In this last scenario, we're going to talk about pointing the MX record to an on-prem server so the on-prem server can do filtering and provide compliance services. 

At the same time, the on-prem server will relay emails to the Internet through Microsoft 365. This mail flow scenario comes up when you're migrating mailboxes to Exchange Online while keeping some mailboxes on-prem. At the same time, you wish to use an existing on-prem filtering and compliance solution. In this case, all emails sent from the on-prem servers will relay through Microsoft 365 out to the Internet. That being the case, the email domain's MX record needs to point to the on-prem server. This mail flow scenario is shown in the diagram on your screen. So, you've now been introduced to all four scenarios where you'll be managing mail flow with mailboxes in both Exchange Online and on-prem. Be sure to familiarize yourself with each scenario in this lesson and with the architecture required for each. For step-by-step details on deploying and managing each type of solution that's been discussed in this lesson, visit the URL that you see on your screen.