online upgrade of in-production Exchange 2013 to 2016, with only momentary down time

Bob_Simons used Ask the Experts™
A bit off topic but completely relevant:
I have a client with a pair of 4-year-old Dell tower servers with Microsoft Volume Licensing copies of Server Standard 2012R2 and the servers have Dell’s better support, so called Pro Support Plus. Dell has recently changed the terms of their support agreement and now they refuse to support any system tht doesn’t have OEM server software installed, with the OEM sticker on the box. Exchange 2013 is now out of mainstream support as of April 2018 and as I said, Dell now refuses to support these systems and I decided it made more sense to just migrate to Exchange 2016 rather than pay retail per hour rates or fighting Dell’s legal department.

I’d be interested in talking with anyone who thinks they could help me get Dell to reinstate the 5-year support agreement that we aid so much for, but that’s not directly relevant here. Meanwhile, Microsoft enterprise support won’t support any product that is out of mainstreams support without paying another $500 per incident fee. But they’d support 2016 under the existing contract.

So, rightly or wrongly, I decided to install Exchange 2016 on a Hyper-V guest and then turn off the 2013 exchange server. If this was a seriously dumb move, I will walk away from the exchange 2016 and try something different.

Which brings me to the technical question(s): how simple is this to do while the 2013 server is in production? The Server 2012R2 Standard host only has only one guest on it but the license allows 2. I want to spin up another 2012R2 guest and install Exchange 2016 on it and initially move the mailboxes while keeping 2013 running. I’m hoping that this means that OWA and ActiveSync will behave like nothing’s changed and I won’t need to do a touch all, especially of the cell phones and off-site laptops.

There are a number of problems with the Exchange 2013 server that I hope I can sidestep by moving the mailboxes to 2016. If not, then I hope the rest of the migration will resolve the issues. One user with a 10-gig mailbox, set to unlimited capacity gets repeated out of capacity errors every 3 to 6 months even with the mailbox down to about 10 gigs. None of the other users has this issue. Another user gets OST “unable to send” errors at a 40-gig mailbox limit even immediately after rebuilding the mailbox. No problems in uncached mode or with OWA. I’m aware of the 50-gig limit and the need to compact the mailbox when using OSTs with mailboxes this big but this happen immediately. Various users lose the ability to search for subject lines and text within emails in both OWA and outlook of varying versions, from 2010 to 2019.

I’ve considered moving to hosted exchange but unless I’m misinformed, Hosted exchange has a 50-gig limit, same as on-prem exchange does if it uses OSTs, which I understand is needed for searching.  So, by itself it wouldn’t solve my underlying problem.

So again, the questions are (a) would a move to 2016 buy me some time to get them onto a document management system that would allow me to greatly  and get the mailboxes smaller, at which point I could move to hosted exchange or on prem 2019; and (b) can anyone help me with doing this or point me to insrtucuitons that would be clear enough that I’d likely be successful
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Distinguished Expert 2018
How many mailboxes you have?
You can get E3 / E5 plans for exchange online which provides you unlimited mailbox quota, though its initially restricted to 100 GB but you can raise request with them to increase quota further
That is better option if you get good enterprise deal from MS

Else you always have option to upgrade to exchange 2016
The process is very straight forward, no downtime is required for this transition

All you need to do is extend AD schema to suite exchange 2016 (you need to ensure that you have at least 2012 domain controllers with 2008 R2 functional level if I am not wrong) and install exchange 2016
Then point your exchange MX and URLs ( and to exchange 2016 and start moving mailboxes gradually

You can navigate to Microsoft Exchange deployment assistant website and answer few questions asked by wizard and it will give you all guide lines and configurations no matter you choose exchange online  / onpremise
If you want to design server sizing of exchange 2016, exchange calculator is also available

If you choose exchange online, you still need to retain one hybrid server (Exch 2013 / 2016) with all roles for mailbox management and you will get hybrid license key as part of exchange online E3 / E5 plans, you should not keep any mailbox on that server and need to use it for purely user management (exchange attributes should be managed through exchange hybrid server only to be remain in supported scenario as per Microsoft)
Seth SimmonsSr. Systems Administrator

how simple is this to do while the 2013 server is in production?

not too difficult if you plan correctly.  i'm in the middle of migrating off exchange 2010 and has been very smooth and transparent migration; nearly all user mailboxes are off 2010 at this point.  also need to look at your mail flow setup to make sure mail gets processed in and out through 2016 and off 2013

would a move to 2016 buy me some time to get them onto a document management system that would allow me to greatly  and get the mailboxes smaller

not necessarily.  there could be other settings in the environment causing the user issues that won't just go away with an upgrade.  if mailboxes are large because users are using it as a repository where by installing something like sharepoint (or similar) will change users' habits by not storing things in their mailbox,  another option is to have enterprise license/CALs for certain users with large mailboxes to have an archive mailbox.  40gb is a bit much and could see how some OST issues can be introduces when approaching that size.

(you need to ensure that you have at least 2012 domain controllers with 2008 R2 functional level if I am not wrong)

it supports 2008 R2 domain controllers; we have that now while doing a 2016 migration
it's the move to exchange 2019 that requires minimum 2012 R2 functional level which I have to deal with shortly
AmitIT Architect
Distinguished Expert 2017

After reading your question, i would suggest you to move to 2016 on-premises. It is supported till 2025. Refer:

Rest you follow typical migration plan. Use Exchange deployment assistant tool, that can create all required steps needed for migration.

Regarding large mailboxes. It is not the mailbox size, it item per folder, which causes more issues. It items per folders are less, you are good. I have mailbox above 100GB. Running smooth from several years.

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