Basic plan to get started with migrating from Exchange 2019 to Hybrid - am I on track?

Question

I've done quite a few initial installations and upgrades/migrations of Exchange going back to Exchange 2000, however, I have never done a hybrid migration. I think I'm making the hybrid migration out to be much more complicated than it is.

We are using Office 365 for everything except mail. We sync with Azure AD Connect. We have a .local domain, but have an additional UPN that matches our public domain, and all users log into O365 with that UPN, which is their public email address. Currently, no user has the Exchange online license on O365, so I know we will need to assign that license once the hybrid is in place.

We have a single on premises Exchange 2019 server running all roles (about 900 users total, 100 staff and 800 students). Right now, we have a Barracuda Spam Firewall that recieves all mail before forwarding to the Exchange server, but we do publish OWA on a different IP address/URL. All outbound mail currently goes through the Barracuda as well.

After doing much reading and research, I believe that I can just start by running the Hybrid Configuration Wizard to go into hybrid mode, and then adding the Exchange Hybrid option in Azure AD Connect.

If I understand correctly, once Exchange online licenses are given to users, they can log into Office 365 and see their mail from the on premises server. And I believe that I can leave my My MX record alone for now and still have mail delivered through the Barracuda.

Is that correct? Once I have mail available on O365, my plan is to change the MX record and autodiscover to go to EOP/O365, and then start moving mailboxes to O365 and use EOP instead of the Barracuda. My understanding is that mail will be available to users in Office 2016/2019 regardless of whether it's on premises or in O365.

Does all of that sound correct for me to get started with the basics to have mail available in O365?

Answer 1

@Brian Hall

no user has the Exchange online license on O365, so I know we will need to assign that license once the hybrid is in place

Yes, if you assign Exchange online license before migration, it will create duplicate mailbox for each user. You need assign license to them after migration.

And I believe that I can leave my My MX record alone for now and still have mail delivered through the Barracuda.

During migration, you could keep MX record to local Exchange on-premises. It is suggested to point MX to EOP after migration. If there exist third party filter tool between Exchange on-premises and Exchange online, it may cause a mail flow issue.

Here are two articles which may be useful to you:

• How to sync on-premises Active Directory to Azure Active Directory with Azure AD Connect?
• Exchange/Office 365 Hybrid Configuration Wizard – step by step guide

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Answer 2

If there exist third party filter tool between Exchange on-premises and Exchange online, it may cause a mail flow issue.

I forgot to mention that although our MX record points to the Barracuda spam filter, we do have a DNS A record to publish OWA on a separate URL/IP address on port 443, so I will need to add inbound port 25 to that firewall rule for Exchange online to communicate directly with the on-prem server using the OWA DNS/URL. It's my understanding that when all mailboxes are migrated to O365, I can stop publishing those.

Answer 3

Check a couple of examples showing how to configure the Exchange Hybrid configuration - https://www.alitajran.com/exchange-hybrid-design-planning/