After months of planning, preparation and migration efforts, you have finally moved from your on-premises Exchange 2010+ system to Office 365. Now you are thinking "do we need to keep our Exchange server(s)?" As with most services, the answer is "it depends".

Having personally been involved in the migration to Office 365 for over 200 organisations, this question about decommissioning the on-premises Exchange server has been asked more times than I can count. My standard answer is that there is no right or wrong answer; it is a matter of preference. Here are the reasons why you may want to keep (or retire) your local Exchange server(s) after an Office 365 migration:

1. Local mailboxes are required for security and/or compliance needs.

Based on your company's needs or compliance requirements, there are certain mailboxes, such as those for finance, accounting or HR, that you may want to maintain on-premises. Keeping your Exchange hybrid environment up and running will allow you to have some mailboxes on-prem and others in the cloud.

2. Application and Device Relays needed

Most organsations have multi-function devices (MFDs) that provide a scan-to-email function for their staff. Additionally, many 3rd party applications require the ability to send email from within the program. While newer MFDs and applications offer this interoperability with MS Office 365, older systems may not support the authentication and/or protocol requirements for sending direct to O365. In these cases, maintaining the Exchange server provides for an on-premises relay to accommodate these legacy systems' send requirements.

3. Public Folder Migration

If you have a lot of public folders (or even a few very large ones) in your Exchange Organisation, there could be a large investment of time, effort and resources to move them to Office 365. Keeping the Public Folders on-premises not only provides additional planning and migration time; but allows you the option to not migrate and just maintain them "as is" while you look to move the data to SharePoint online.

4. Management (And this is the big one)

The biggest reason that a company may opt to keep an Exchange hybrid server on-premises is management. Once a mailbox migration has been completed and the Exchange servers removed, administrators lose the ability to modify mail-related attributes in a GUI; instead relying on Azure PowerShell and/or ADSIedit/Active Directory User Attribute editing. While this may not sound like a big deal, imagine that each time you want to add or modify a user's email address of aliases (such as in the case of marriage or divorce), or if you need to update membership of a group, you have to go into the object's AD account properties and make changes directly by hand-typing them.

By keeping that Exchange hybrid server around, you can continue to create, modify or delete mail related properties for users and groups, just as you always have.

As stated in the opening, there is no right or wrong choice regarding keeping or decommissioning the Exchange server once a migration to Office 365 is completed; it is just a matter of choice. Hopefully your Exchange team will weigh all of the pros and cons before deciding to pull the plug on your Hybrid server!

Neal Zimmerman is Cloud Enablement Services Manager at US managed services provider Binary Tree.