Article IT security and cybersecurity
Bartek Kamiński | 2026-01-07

Email migration project to Microsoft 365

The project was carried out for a manufacturing company that had a local Microsoft Exchange 2016 server and a relay server based on the Linux operating system. The relay server ran additional features such as antivirus and antispam. Another server ran a proxy server for OWA and ECP.

Migration of all mailboxes from Exchange 2016 to the Microsoft365 cloud - decision after the end of support

Due to the end of support for Microsoft Exchange 2016 in October 2025 and the resulting lack of security updates after that date, we offered the customer various migration options. One option was to migrate to the Microsoft 365 cloud, and the customer selected this option. All mailboxes from the on-premises server were migrated.

Email migration process to Microsoft 365

First, we configured the connection between the local Active Directory service and the tenant in the Microsoft cloud, and launched cyclical object synchronization, which ensured, among other things, the ability to log in to mailboxes in Microsoft 365 services with the same password as to local accounts, e.g. Windows desktop systems.

In the next step, we launched a Hybrid connection between the on-premises Exchange server and Microsoft 365 on the Exchange server. We updated DNS entries to handle mail through Microsoft servers, added MX entries with a lower priority than the on-premises server, added DKIM and DMARC entries, and updated the SPF entry. In the Microsoft service, we reconfigured the connectors created by the wizard, needed for the simultaneous operation of both mail systems and the exchange of data between them (mail sent from M365 to the company domain should be sent to the relay server, i.e. the local server).

After confirming mail flow from and to the local and online servers, we migrated user mailboxes. The migration was performed using Microsoft tools. The entire process was seamless. After mailbox migration, users received a notification about the changes made by the administrator; they only had to disable and enable the Outlook email client. After completing the mailbox migration, we updated and removed unnecessary entries on the DNS servers responsible for mail handling. The local servers were taken offline for a week to verify and confirm smooth operation. After this period, the old servers were depromoted and completely removed from the organization.

Additional project assumptions

Additionally, the migration project involved implementing a backup solution for services hosted in the Microsoft 365 cloud, including the migrated email. Veeam Backup for Microsoft 365 was used for this purpose. The locally installed software performs periodic backups of the company's infrastructure. A new repository for backing up Microsoft 365 was added.

Following the migration, the company also began using other Microsoft 365 services, such as Teams, for fast communication between employees and collaborating companies.

The next steps include migrating data from local network drives to SharePoint. The freed-up server resources can be used for other services, such as database servers, used locally.

Summary

Switching to Microsoft365 means more than just cloud access, it also means standardizing office applications. With an Office365 subscription, every user receives the same, latest version of Office, ensuring:

  • Uniformity of the work environment – ​​everyone uses the same tools
  • Automatic updates – software is constantly updated to the latest versions without additional costs or manual intervention
  • Rule out version issues – get rid of the problem of different Office versions

In practice, this means greater efficiency, a reduced risk of compatibility issues, and simpler license management. If you're planning to migrate to Microsoft 365, contact us!

Bartek Kamiński - Team Leader w Support Online
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