Depending on which iteration of Exchange you're running, there may be increased urgency regarding an Exchange Server...
migration to a newer version. With the Exchange 2007 and 2010 versions in extended support, you'll need to consider your options and formulate a plan.
Microsoft currently supports four versions of Exchange Server: Exchange 2007 and 2010 are legacy versions and provide the basis of modern features used in newer Exchange products, such as PowerShell management and continuous replication. Exchange 2013 has proven to be a suitable successor to the 2007 and 2010 versions, and Exchange 2016 further builds upon its reliability improvements and cloud capabilities.
Exchange Online, a do-it-all hosted messaging platform, is offered as part of Office 365. This platform always runs the latest version of Exchange, and although users perform day-to-day user and mailbox administration, Microsoft manages the server-side tasks for you.
Considerations before an Exchange Server migration
Choosing a version of Exchange isn't just about aligning the benefits of the respective version with your organization's needs. There is a long list of factors to consider before planning a migration of Exchange Server.
If you run Exchange 2003, you need to jump to Exchange 2010 and then 2013 or higher. This may require twice the amount of hardware than what you currently have. The same effort may be required for those running on Exchange 2007 -- a move to Exchange 2016 first requires an upgrade to 2013.
Simplicity alone shouldn't be a deciding factor for your Exchange Server migration plan, but budget and time constraints may rule out a complex and costly transition. These restrictions could narrow your options.
The desktop office client can also have a bearing on the best version of Exchange. If your organization runs on Office 2007 and is not ready to upgrade or purchase licensing for newer versions, you will only be able to migrate to Exchange Server 2013 and not Exchange Server 2016. Conversely, if you plan to deploy Office 2016, you will need to run Exchange 2010 or higher.
Third-party application integration for line-of-business applications is often a stumbling block in Exchange and Office 365 migrations. Often, organizations don't adequately test third-party tools, such as server-side integrations or client-side integrations. Applications that rely on the Messaging Application Program Interface/CDO library must be compatible with the latest version of the library to work with Exchange 2013; these apps will not work with 2016.
Backup software support for Exchange often lags behind the release of the latest version of the technology. If you deploy the preferred architecture, then backups are not an issue; however, if you deploy a traditional infrastructure that is regularly backed up, you need Exchange-aware backup tools. These must integrate with Windows and quiesce the file-system during backups; after a successful backup, they expunge unneeded log files.
With a cluster that uses database availability groups, the database could be running on multiple nodes. Restores often require deep integration to ensure it is easy for an admin to restore data into a user mailbox. It is often takes a long time for the backup vendors to support a new version of Exchange, and might even require a full upgrade of the backup system.
If you use existing hardware, such as a virtual infrastructure, you may have limited resources. Exchange 2013 and 2016 use considerably more CPU and RAM resources than previous versions, and you may struggle to accommodate this workload alongside existing VMs. An investment in additional RAM or an additional virtual host, however, may be a better investment than migrating to a legacy version of Exchange.
Those planning a move to Exchange Online must consider third-party application integration and clients, as well as Internet bandwidth and availability. Business-as-usual requirements for Exchange Online are fairly low -- potentially less than 10 MB/sec for a small, 200-user organization. However, if you are unable to achieve the required bandwidth, or are using a third-party tool to migrate and must re-download the offline cache, this could increase your bandwidth requirements in the short term.
Exchange Server versions
Exchange 2007 and 2010 are in extended support, so don't consider either option for your Exchange Server migration plan unless there is an unchangeable dependency, such as a legacy application. Implementing either of these versions could be an exercise in futility, as you can expect to need another migration again shortly thereafter. Exchange 2007 in particular is an unwise choice, as it does not provide a direct migration route to Exchange 2016.
If you want the best compatibility with third-party applications, then Exchange 2013 may be your best option. The upgrade path from Exchange 2007 or 2010 to Exchange 2013 is clear, and ensures a future migration to Exchange 2016 will be straightforward.
Organizations currently running Exchange 2010 -- and willing to wait a short time -- should consider Exchange 2016. This version of Exchange owes heavily to Exchange 2013 and shares more than a passing resemblance with the preceding version. However, it provides a much greater range of user-facing features, such as a vastly improved online Outlook experience.
If migrating to a new version of Exchange on-premises worries you, then a move to Exchange Online, hosted by Microsoft in Office 365, might be a better alternative. Exchange Online runs in Microsoft's data centers, so you'll never need to perform another in-house upgrade.
Perform some assessments to understand what you have before beginning your Exchange Server migration. My Exchange Environment Report can assist, and is available from Microsoft's Technet Gallery. This resource will generate a comprehensive report with statistics from your environment.
You will also need to understand the message send and receive statistics for your environment. Use the Generate Message Profile script to collate this information.
Before purchasing any hardware, understand what kit is required. The Exchange Role Requirements calculator for Exchange 2013 provides this information.
The Exchange Bandwidth calculator is a script that helps you understand the bandwidth users will need. It is especially useful for Exchange Online deployment planning.
You can also create a custom deployment guide using Microsoft's Exchange Deployment Assistant. That tool covers Exchange 2010, 2013 and Exchange Online.
Six guidelines for Exchange 2016 installation plans
Exchange 2016 features and capabilities
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