Exchange 2016 and Migration to M365

[Mayo, Bill]

We have been in planning with a third party for migration to M365 for some months now. We still have Exchange 2016 and there have been debate about what you can or cannot do with this version of Exchange. Microsoft documentation seems to suggest some things that I thought were not true, so I am seeking to understand. I am also not sure that I trust the third party as a completely reliable source of information. Can anybody answer these questions definitively?

 

1. Can you or can you not migrate directly from Exchange 2016 to M365 now that Exchange 2016 is past end of support? It was my understanding that you could not, but there are differing opinions driven a lot by Microsoft documentation.
2. As a sort of sub-question to the above, does Microsoft actually block you from migrating, or is it just not “supported”—meaning they won’t help you if run into issues?
3. Assuming you cannot migrate from Exchange 2016, can you simply install an Exchange SE server in your environment and then use it as an interface to migrate the mailboxes hosted on 2016 servers? Or, do you have to fully migrate all mailboxes from 2016 to SE before migrating to M365?
4. A question I still regularly debate is whether you have to keep an on-premise Exchange server or not after migrating to M365. My longstanding understanding is that you do, although Microsoft has made it so that it could be shutdown. However, something I read makes me think that this answer is driven by whether you are keeping AD on-premises or not. Is that accurate?

 

Thanks to anyone that can help confirm.

 

Bill Mayo

[Michael B. Smith]

I presume that you are dual-hybrid. Hybrid AD and hybrid Exchange. My answers are correct for that environment.

 

[1] Yes, you can – for now. MSFT has not yet disabled connectivity from E2016, and they haven’t announced it, as far as I know, but it is just a matter of time. MSFT strongly wants everyone either in the cloud or on Exchange SE – those pump their bottom line. Other editions/versions do not.

 

[2] If you pay for a case, you get “best effort” support. That being said, I’ve not had to open a migration case in years. To answer your question specifically – it’s just not supported.

 

[3] You can use an Exchange SE server as the migration endpoint and it will proxy to the E2016 server. I did this quite recently with an E2016 server to an E2010 server. This worked fine. We did try migrating some to the E2016 server first, to see if it made a difference, but other than being slightly faster (which was probably just because of the hardware difference), we found no recognizable difference in the migration experience.

 

[4] This is a complex question and I’ll give you a consultant’s answer: it depends. Long story short – must you? No, you don’t have to. HOWEVER, if you are going to keep the source of authority for your users/groups/etc. in your on-prem AD, then you should – otherwise you’ll be required to do Exchange administration via PowerShell. Doable, but complex for most people. If you are ready to move the source of authority for all Exchange objects to the cloud, then no, you don’t need it. However, I strongly recommend that you do that migration separately from your M365 migration and also do it carefully and slowly. I find that most organizations are really not ready for this, even though they would like to be (for example – mail-enabled security groups can be very challenging to deal with and Microsoft’s recommendation to convert all DLs and MESGs to M365 Groups just complicates things - IMNSHO).

 

As a secondary item, you might find eliminating that last server difficult just because of mail relay; the solutions provided by MSFT are not complete. For some things, their solution is “replace the hardware” which isn’t always feasible.

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