Fully Migrating Exchange Server 2019 to O365

Hi Nasir,

Exchange Server Subscription Edition will be available from July 2025. You can do an in place upgrade from Exchange 2019 directly. Please find below URL for more details.

Upgrading your organization from the current versions to Exchange Server SE | Microsoft Community Hub

You may keep one Server for Management purposes and move all your SMTP Traffic to Office 365. You need to make sure all the Application, Printer and Scanner supports Modern authentication before moving it to Office365 SMTP.

Regards,

Vimod

Exchange 2019 to Office 365 Migration

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TL;DR
For ease of management, it might be beneficial to keep the latest version of Exchange in Hybrid config and keep it up to date all the time.

Here are several links that support the recommendation to leave at least one Exchange hybrid server on-prem:

Azure AD Connect and removal of on-prem Exchange 2010 server
https://docs.microsoft.com/en-us/answers/questions/9221/azure-ad-connect-and-removal-of-on-prem-exchange-2.html
 
Removing Your Last Exchange Server FAQ
https://techcommunity.microsoft.com/t5/exchange-team-blog/removing-your-last-exchange-server-faq/ba-p/3455411
 
How and when to decommission your on-premises Exchange servers in a hybrid deployment
https://docs.microsoft.com/en-us/exchange/decommission-on-premises-exchange
 
Decommissioning your Exchange 2010 servers in a Hybrid Deployment
https://techcommunity.microsoft.com/t5/exchange-team-blog/decommissioning-your-exchange-2010-servers-in-a-hybrid/ba-p/597185

Office 365 and Dirsync: Why should you have at least one Exchange Server on-premises
https://mymicrosoftexchange.wordpress.com/2015/03/12/office-365-and-dirsync-why-should-you-have-at-least-one-exchange-server-on-premises/

Exchange Server Roadmap Update
Exchange Server Roadmap Update | Microsoft Community Hub


Some of the links might be talking about older Exchange versions, but from perspective of Hybrid config that does not make a difference. You can remove Exchange and manage everything through either scripting or ADSIEDIT, but that is more on the side of management, not functionality.

Generally it's recommended to keep the on-prem server if you are using it for relaying because it's required for managing on-premises attribute values (remember that you are syncing accounts from on-prem to O365, so most attribute management needs to be done on-premises). There are restrictions about relaying directly to EXO (You can see details on this here), and you need to ask yourself how comfortable your admin/support teams are with using PowerShell to manage Exchange attributes, as this is the only supported option available to you if you decommission your on-prem Exchange server. Details on some restrictions can be found in this document