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Which Edition of Exchange Server 2016 to Deploy?

If you’re planning an Exchange Server 2016 deployment you will need to consider which edition of the product to deploy on your servers.

For Exchange Server 2016 there are two editions of the server product itself, and there is only one difference between them which is the number of mounted databases per server.

  • Exchange Server 2016 Standard Edition – maximum of 5 mounted databases per server
  • Exchange Server 2016 Enterprise Edition – maximum of 100 mounted databases per server

Microsoft’s definition of a “mounted database” is:

A mounted database can be an active mailbox database that is mounted for use by clients, or a passive mailbox database that is mounted in recovery for log replication and replay. While you can create more databases than the limits described above, you can only mount the maximum number specified above. The recovery database does not count towards this limit.

Here’s a few examples. In this example a single Mailbox server running Standard Edition has 5 mailbox databases. All 5 databases will be able to mount, and an additional recovery database can also be created and mounted for any data restoration scenarios.


The same server running Standard Edition with 6 mailbox databases will not be able to mount all of the databases at the same time. However, if it is running Enterprise Edition it will be able to mount all 6 databases, or up to 100 databases.


What about a database availability group? DAGs can have up to 16 members, and each member is limited by the edition of Exchange Server 2016 that is installed. So a Standard Edition DAG member can host up to 5 active or passive database copies, and an Enterprise Edition DAG member can host up to 100 active or passive database copies. The DAG itself is only limited by the capabilities of all of its members. A DAG made up of 16 Standard Edition members, with each database having 4 copies, could therefore host up to 20 databases.


To be clear, there is no requirement to run Exchange Server 2016 Enterprise Edition just because you’re deploying a DAG. The choice of server edition is purely driven by the number of mounted databases each server will be hosting.

For the Edge Transport role, given it does not host any databases, it makes sense to use a Standard Edition server license.

When you purchase your Exchange Server 2016 server licenses you’ll be provided with a license key that needs to be entered on the server. The license keys determines which server edition is installed, there is no different in installation media or installation method for each edition. All servers are first installed as a Trial Edition, and then you add your license key after installation is complete. You can upgrade from Trial to Standard, or from Trial to Enterprise. You can also upgrade from Standard to Enterprise. However, you can’t downgrade from Enterprise to Standard without completely reinstalling the server. This means it is feasible to initially license your servers as Standard Edition, and then later upgrade them to Enterprise Edition if your environment scales up (e.g. if there is a corporate acquisition or merger).

As a final note, the information above applies only to the server licenses. The Client Access Licenses (CALs) are considered separately, and have no impact on the server license you choose to deploy and vice versa.

Paul is a Microsoft MVP for Office Servers and Services. He works as a consultant, writer, and trainer specializing in Office 365 and Exchange Server. Paul is a co-author of Office 365 for IT Pros and several other books, and is also a Pluralsight author.
Category: Exchange Server


  1. Sander says:

    “A DAG made up of 16 Standard Edition members, with each database having 4 copies, could therefore host up to 20 databases.”

    Isn’t it 16 databases? Correct me if i’m wrong 🙂

    1 database and 4 copies = a total of 5
    5 active or passive databases per member * 16 (members per dag) = 80
    80 / 5 = 16

  2. Miguel Rubio says:

    I think i don’t understand the database part, with a standard license i can just get 5 mailboxes?

  3. Mike says:

    Hi, Licencing is not clear to me. Can you help me with the following? We´d like to migrate to ms exch.
    Should we buy cals for win server 2012 with AD, too? Or just cals for exchange? I mean 30 users. Is Open program good for us?
    Thank you for your answer

    • Dan says:

      You need to licence Windows Server (and CALs) and Exchange Server (and CALs). CALs should be licensed for the functionality required alongside the Server licence. You need to also account for access by the type of CAL (User or Device). Best bet is to go for a User CAL so that you cover all products that you may use (or may be used in conjunction with the server, such as a multi-functional printer for example).

      Every user/device must be covered for any direct/in-direct access to the server hosting Exchange.

  4. Andy says:

    Thanks Paul,

    thats helped me make the decision on versioning. the MS site wasnt very clear this time.

    All the best!


  5. sam says:

    Hi Paul,

    Can we have different domain DBs in one exchange server ?

    For example,


    Though exchange server is attached to one domain, like “mail.samnco.com”. pls advise.

    • Yes, you can host different Accepted Domains in the org, and have those recipients sit in the same database.

      The Accepted Domains for the org, and the AD domain name that the server is joined to, are two separate and independent things.

  6. Dmitry says:

    IMPORTANT!!! Database size is limited to 1 TB in Exchange Standard.
    We encountered this issue today morning, when we configured DAG on our Exchange Standard cluster. Our 1.1 TB database failed to mount, displayed error about database size.

    We had to apply a workaround from Microsoft , which mounts databases in -force mode. Not a good solution though, since one can mount a potentially damaged database like this.

    Now we are splitting database to smaller pieces.

  7. Hassan says:

    What is powershell commandlet if i want to set mailbox size limit for each user 10gb. Commandlet should be for bulk users. thanks

    • Josh G says:

      Just set the mailbox size limit at the database level and have all mailboxes use database default quota (all mailboxes by default use the database quotas anyway)

      Set-MailboxDatabase DatabaseName -ProhibitSendReceiveQuota “10 GB”
      Get-Mailbox -ResultSize unlimited | Set-Mailbox -UseDatabaseQuotaDefaults:$True

  8. Fabiano Pereira says:

    Hi Paul,

    To make a High Availability of Exchange Server 2016. What server licenses i need?
    For 2 Servers, 2 Licenses of Exchange Server only? In this version i don´t need of SQL Server license or it was included?

  9. mk says:

    Dear Sir,

    Can I convert MS Exchange server 2016 Evaluation to Licensed?

    Please find below my exchange server version and trial expiry details. Can you please validate and guide me from it. Thanks a lot,

    Get-ExchangeServer CAP-DC | Format-Table Edition,*Trial*

    Edition IsExchangeTrialEdition IsExpiredExchangeTrialEdition RemainingTrialPeriod
    ——- ———————- —————————– —————————
    StandardEvaluation True False 61.05:18:04.1516299

  10. Ian says:

    Someone told me if I’d like to use VOIP and Exchange integration, I need to purchase enterprise version. That means standard version can’t do that ? Is this correct ?

    • This article is about the server editions, which only differ in the number of mounted databases they can host, per the article.

      Unified Messaging is a feature governed by the Exchange CALs you purchase.

  11. Michel Turgeon says:

    Hello Paul,
    The recovery database does not count towards the limit of 5 mounted DBs. Is the same statement also true for the Transport Database?
    Thank you

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