Load Balancers

Exchange Cumulative Update 8 Released

Exchange CU8

Microsoft recently released Exchange 2013 Cumulative Update 8 (CU8). This release follows just three months after Cumulative Update 7 (CU7), which we discussed in February. Like the previous updates, CU8 can be used to update a previous deployment of Exchange Server 2013 or install a new instance from scratch. All of the changes that appeared in CU1 through CU7 are included in CU8. There is no need to deploy the previous updates before CU8.

As outlined in our CU7 post, the cumulative updates cannot be removed after they are installed. Also, the Active Directory Schema is updated during the installation of CU8. For this reason, it is vital to have reliable backups before deploying the update. Note that you also have to restart each Exchange Server that CU8 is applied to. Therefore, you will need to plan for some service interruption.

What benefits does CU8 bring?

As with each of the cumulative updates, there are a lot of additional features and fixes included in CU8. Microsoft details them all in this knowledge base article. Some of the new or enhanced features in this release are as follows:

• Contact Modern Public Folders favourites and Calendar features are now accessible in Outlook Web Access (OWA).
• Batch Migration of Public Folders to Exchange Server 2013 improves migration throughput.
• The number of supported Public Folders has increased for on-premises deployments. This is one of the most important enhancements. When migrating from legacy versions of Exchange 2007/2010 to Exchange 2013 CU8, there can now be up to 500,000 public folders. This is a 200% increase from CU7. After your migration is complete, Exchange 2013 CU8 can go on to support up to 1,000,000 public folders. A 400% increase from CU7.
• Smoother migration for Exchange Active Sync (EAS) clients to Office 365 with automatic profile redirect upon successful migration (Exchange ActiveSync Client must support HTTP 451 redirect).

In addition to the features above, the CU8 release fixes the following issues:

• Outlook client cannot download an Outlook Address Book (OAB) file in a mixed Exchange Server 2013 and Exchange Server 2010 environment.
• Mailbox quota warning messages are not sent out to users after you migrate from Exchange Server 2010 to Exchange Server 2013.
• Default folders are duplicated after you migrate mailboxes to Exchange Server 2013.
• SMTP is not transported over TLS 1.1 or TLS 1.2 protocol in an Exchange Server 2013 environment.
• Mails can be spoofed in Office 365 or in an Exchange Server 2013 environment.
• Recurring events in Calendar that span a Daylight Savings Time change are not adjusted on all ActiveSync devices.

These fixes, and the others outlined in the Microsoft release notes, make CU8 a recommended upgrade for all Exchange Server 2013 sites.

Microsoft Exchange Server 2013 deployments have servers with different roles. Some different considerations are appropriate for these roles when deploying CU8.

Updating on Client Access Server (CAS) Role

Organisations configure one or more CAS servers with different load balancing solutions to provide high availability and resilience for client connection requests. You need to make sure that user connections are not affected while upgrading the servers to CU8. Below are some of the steps to follow:

1. If your CAS servers are behind a hardware load balancer, it is a good practice to drain the old connection to the specific server from the load balancer and then disable for any new client connections before performing the CU8 upgrade. Enable the CAS server in the load balancer again once the upgrade is complete.
2. If CAS servers are load balancing using DNS round robin, then remove the DNS entry for the CAS server and then add it back after upgrading. DNS replication would need some time to propagate after adding and removing the DNS entry.
3. If the CAS servers are configured with Windows Network Load Balancing, then start the Network Load Balancing Manager, right click on the CAS server, and select the option ‘DrainStop’. This option will drain any pre-existing connections and will bring the server into a stopped state. Resume the server once upgrade is complete.

Updating Mailbox Server Role

Exchange 2013 Mailbox Server roles contain the mailbox databases. To ensure that mailbox access is not affected during the upgrade, it is recommended that the mailbox server being updated be placed in maintenance mode. It is then possible to move the database on the server being upgraded to another mailbox server in the Database Availability Group. This Exchange World blog post on TechNet has details and instructions on how to place the server into maintenance mode in various scenarios.


With great new features and enhancements, plus loads of bug fixes, CU8 is a must-have update. It is important to test the deployment in a lab or test environment before deploying to production. Remember, once you install the update it can’t be removed. But don’t let that stop you. Just plan the upgrade properly.

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