Your checklist for a successful Office 365 Exchange Online migration

Migration to Office 365 Exchange Online has been around since the early stages of cloud adoption. Most of the times it has been used as the stepping stone for organizations to make their first move to the cloud, starting from their mail system.

It is always important to create a proper action plan outlining all required steps in detail to ensure you won’t run into any unpleasant surprises.

As such, I outline below the most important steps that work as prerequisites for a successful migration:

  • Ensure that all Outlook clients within your organization are at least Outlook 2010 SP3. Older versions won’t connect to Exchange Online services. Keep in mind that even this product version won’t be able to connect after the end of Q2 of 2021. Picking one of Office 365 plans which contain the offering of the Office Suite would be a good choice moving forward.
  • Prepare to add records in the public DNS zone of your domain. I always find it more convenient when organizations control their records since contacting a third-party provider isn’t always fast. Whatever the case, you will need to be flexible in updating your public DNS records at this stage.
  • Add an SSL Certificate. A third-party SSL certificate from a trusted public Certificate Authority is required to establish the Migration Endpoint between your on-premises Exchange Server and Office 365.
    That means that any self-signed SSL certificate won’t work and the connection to Microsoft’s datacenters would always fail.
  • Clean up your Active Directory to avoid running into issues. Once you begin the migration, you would want most of the mailboxes to complete their moves without any issues.
    What proves to be very helpful on this is to review the user accounts in your Active Directory in an attempt to find errors. Typical errors could be:
    • Mailbox Delegations to disabled or non-existent users. This will surely blow up migration for certain mailboxes since it will stop it from running numerous times. The worst thing about this? The undefined messages. You rarely get an error message with a good explanation during the migration stage.
    • Forgotten permissions assigned either on database or mailbox level. At some point, someone from the IT department could have set permissions to their username, but this account could be disabled or deleted at the time of the migration. This could create issues to the migration batch as well.
  • Get your users to delete unnecessary content from their mailboxes. Sure, that obviously makes sense, but it doesn’t mean it applies all of the times! You will also want to instruct the users to Empty the Deleted Items folders too! Trust me; this action could save you both bandwidth and space!
  • Search for PST files that are attached in the current Outlook profile of your users. As a post-migration task, you will need to create new Outlook profiles for your users so they can connect to their Exchange Online mailboxes and you don’t want some of them to realize they miss their PSTs right after the migration completion. Review and enumerate them before the migration so you can either reconnect them to the new profile or upload them to the new Exchange Online mailbox.
  • Pick a strategy for creating new Outlook profiles for your users. While this is actually a post-migration task, it would be wise to make your mind on this before you start the migration. Depending on the size of the organization as well as on how you like to do things, you can either create new profiles by Group Policy (you will need .admx extensions) or create them manually.
  • Review the on-premises devices/hosts that use the local Exchange server as an SMTP relay to deliver notifications. That kind of devices could be multifunction devices, printers, scanners etc. Most of the times, there is a dedicated connector in the Exchange server that allows for relaying in port 25 withing your LAN ranges. You will need to modify these settings to reflect the changes after the migration.

Following most of the above guidelines could prove vital for a successful migration.

You are always welcome to share your ideas on enriching this list!

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