Can You Remove Your Last Exchange Server?


By Cameron Brandon, Structured Sr. Systems Engineer, Microsoft Exchange —

One of the most popular and effective ways to migrate your mail to the cloud is through the use of the hybrid configuration, which establishes an organizational relationship between your on-premises Microsoft Exchange Servers and Exchange Online. This allows for seamless staged migrations where you move all mailboxes in batches to the cloud.

A common question Structured receives is whether you can decommission your on-premises Exchange Servers after a successful migration. While it is best practice to keep an Exchange Server in the organization to manage mail-related attributes, there are a few things you need to consider before continuing.

1. Provisioning Users

If you continue to sync objects with Microsoft Entra Connect (formerly Azure AD Connect) — something we highly suggest you continue doing — you may find the process of provisioning users has changed, now that you no longer create mailboxes on the Exchange Server. In a hybrid, some organizations create a local mailbox for a new user and immediately migrate it to the cloud. The alternative is to avoid the mailbox-migration step by creating a remote mailbox. This is done in the Exchange Management console or in the Exchange Management Shell. But without an Exchange Server, those two methods are not possible. The reason for doing this is to populate the mail-related attributes in Active Directory for the user – something that isn’t done if you simply assign a license in Microsoft 365 to a synced user; the settings never get written back to local AD.

Consistency is the key, so you want to provision future users in a manner similar to the existing users. That means adding the necessary attributes to their account, such as:

  • msExchRemoteRecipientType:  1
  • msExchRecipientDisplayType:  -2147483642
  • msExchRecipientTypeDetails:  2147483648

These settings can be scripted with the Set-User command and incorporated into your user provisioning process.

2. Modifying Mail Attributes

For years you’ve been provisioning users and modifying attributes within Exchange – which is essentially a front end to Active Directory. The most common task is adding additional SMTP addresses for a user. Even though the mailboxes are located in the cloud, you are unable to modify the simplest of attributes in Microsoft 365, resulting in an error like this:

Without an Exchange Server, you can still make these modifications, but you’ll do so in Active Directory Users and Computers using the Attribute Editor, which is a less user-friendly experience.

3. SMTP Mail Relay

It is very common to have numerous multi-function devices (like printers) that scan to email which are configured with the address of the local Exchange Server. These will need to be configured to relay off Exchange Online, and there are a few options to consider, like whether the destination recipient is a mailbox in your organization or you’re relaying off Exchange Online to an external recipient.

4. Distribution List Management

Once mailboxes have been migrated to the cloud, the unfortunate byproduct of this is that owners of distribution lists can no longer manage group membership. When your source of authority is local Active Directory by virtue of using Microsoft Entra Connect to synchronize identities to the cloud, a cloud-based user is no longer able to contact the on-premises Exchange Server to modify the DL. This means your IT team will need to make the changes in Active Directory which will then sync to the cloud. But do you want your IT team to be responsible for managing all distribution list membership for your organization? The alternative to this is migrating your distribution lists to cloud-based, which will then allow owners to manage membership again.

Conclusion

As you can see, there are several factors you must consider when deciding whether to decommission your on-premises Exchange Servers. Structured works with its customers and their unique environment to educate them on the ramifications of removing these servers. We offer a Proof of Concept (PoC) to determine whether your team is amenable to the new user-creation process and daily mail-related management tasks, and then perform the removal process with precision and experience. Contact your Structured account manager or email info@structured.com to get started.


About the Author

Cameron Brandon has more than 20 years of experience in the IT industry. He specializes in on-premises Microsoft Exchange, Exchange Online, Microsoft 365 and messaging migrations. He has performed several Office 365 migrations from various sources, but most popular is the hybrid staged migration allowing for proofs of concept, as well as staged migrations in batches to migrate users in manageable groups. Mr. Brandon also is experienced in fine-tuning of security, compliance, and retention policies to help customers meet regulatory requirements.