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Exchange 2016 CU1 overshadowed when mailbox anchor drops

Microsoft released updates for all supported versions of Exchange Server. The updates cover issues with mailbox anchoring in Exchange 2013 and improvements to lagged database copies.

Microsoft supports four versions of Microsoft Exchange Server, so it's no surprise that the Exchange 2016 CU1, Exchange 2013 CU12 and update rollups for Exchange 2010 and 2007 made for a big release in March 2016.

Due to the coexistence scenarios that Microsoft supports for different Exchange versions, no user can run more than three of the abovementioned versions in a single organization. If you manage Exchange for multiple organizations in various versions, all four updates might affect your users. Here's what do you need to consider with so many updates released in a single quarter.

Update rollups for Exchange Server 2007 and 2010

Let's start with the simplest updates, those for Exchange 2007 and 2010.

Extended support for Exchange Server 2007 and 2010 means no more non-security fixes, new features or design changes will be made to those products, leading to Exchange 2010 Service Pack 3 Update Rollup 13, and Exchange 2007 Service Pack 3 Update Rollup 19.

In reality, any update carries the risk of bugs, and doesn't guarantee the newest CU will be more suitable for deployment than the last version.

Both versions received an update to the S/MIME control for Outlook Web App to make it SHA-2 compliant. Functionally, the control is still the same, but has been signed with a SHA-2-compliant certificate, due to the security algorithm SHA-1 being considered insecure compared to the cryptographic SHA-2.

If your Exchange deployment uses S/MIME, then you simply need to deal with supporting the end users to reinstall the new S/MIME control. There is nothing of concern or impact for Exchange 2007 or 2010 customers beyond that, and you can plan your server upgrades at a convenient time of low Exchange usage.

Exchange Server 2013 CU12

Exchange Server 2013 and 2016 are both in mainstream support, which has no limitations on the types of updates or changes you can expect to see.

Cumulative Update (CU) 12 for Exchange 2013 contains the same S/MIME update as the other March 2016 releases. More significantly, CU12 rolls back a change made in Exchange 2013 CU11 referred to as mailbox anchoring.

In Exchange 2013 CU11, Microsoft attempted to fix one of the challenges of working in multiversion Exchange organizations by anchoring PowerShell sessions to the server hosting the mailbox of the user for that PowerShell session. For users with no mailbox -- which is typical and actually a best practice for administrative users -- the anchoring feature instead selected an arbitration mailbox. While this change did resolve some issues with using PowerShell to manage multiple versions of Exchange, it caused far more problems than it solved. Administrators were forced to move their admin account's mailbox to different servers for server-specific administrative tasks, and many third-party products such as backup tools failed completely.

Exchange 2013 CU12 reverses the mailbox anchoring change, so any administrator who upgraded their Exchange 2013 servers to CU11 should look at upgrading to CU12. Furthermore, if you declined to update from CU10 due to the issues that arose with CU11, now consider upgrading to CU12 and skip the mailbox anchoring problems entirely.

Exchange Server 2016 CU1

Exchange 2016 CU1 is the first Cumulative Update released for the latest version of Exchange. This is a significant milestone; many administrators prefer to wait for the first major update to an Exchange version before they consider deploying it. As there are no service packs planned for Exchange 2016, only cumulative updates, CU1 fulfills that "wait for the first update" assurance those users need.

In reality, any update carries the risk of bugs, and doesn't guarantee the newest CU will be more suitable for deployment than the last version. Exchange 2016 CU1 is a mixed bag, in that respect. Exchange 2016 CU1 contains the same S/MIME update as the Exchange releases described above. And although Microsoft originally planned to include the same mailbox anchoring change as Exchange 2013 CU11, it was removed from Exchange 2016 CU1 due to the problems customers experienced with that change.

Under the hood, Exchange 2016 CU1 delivers lagged database copy enhancements that did not make it into the release to market of Exchange 2016. With CU1, lagged copy play down, which is the automatic replaying of the uncommitted transaction log files into the lagged database copy, will be deferred if the disk hosting the database copy is under heavy load at the time. This change prevents lagged copy play down from causing a performance issue that may impact active database copies hosted on the same disk. Exchange 2016 customers who operate lagged database copies should consider CU1 for deployment.

Keep hybrid Exchange environments supported

If you are running a hybrid configuration with Office 365, or using Exchange Online Archiving, the March 2016 releases for Exchange will require you to run at least Exchange 2013 CU11 or CU12, or at least Exchange 2016 RTM or CU1, to remain supported by Microsoft.

Exchange 2016 CU1 does introduce at least one new bug, with Microsoft warning that customers running Edge Transport Servers may see email messages rejected by recipient validation even when sent to valid email addresses.

Generally speaking, you should thoroughly test updates before you deploy them to your production environment. Even though Microsoft validates Exchange 2013 and 2016 code by deploying it to the cloud first, the developers can't guarantee a trouble-free deployment in on-premises Exchange environments where many other factors come into play. Testing should include validating compatibility with any third-party products that integrate with your Exchange environment, and any business-critical workflows that rely on email.

In the servicing model for Exchange 2016, both Exchange 2016 CU1 and RTM are currently supported by Microsoft, so customers are not under any pressure to upgrade immediately.

Get more information on the updates here.

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