One of the major benefits of migrating to Office 365 is the ability to migrate users to cloud-hosted Exchange. This takes the burden of Exchange administration off your plate, and gives your users the reliability and flexibility they need to get their work done from anywhere.
The simplest way to move from on-premise Exchange to Office 365 is to do a cutover migration. This process moves all of your users’ mailboxes at one time, and allows you to immediately decommission your on-prem Exchange servers once the migration is complete. You can perform a cutover migration as long as you’re running Exchange 2003 or later, and you have fewer than 150 users to migrate.
Prepare Your Exchange Environment for Migration
Office 365 talks directly to your Exchange server to handle the migration. To allow this, you’ll need to enable Outlook Anywhere (RPC over HTTP), and make sure that it is accessible from outside your network. Also, you’ll need to set up Outlook Anywhere to use a publicly trusted cert for HTTPS.
Next, you’ll need a user account that has full access to all on-premises mailboxes. If you don’t already have an account with these permissions, you’ll need to create one — it can be deleted after the migration is completed.
You’ll need to migrate any mail-enabled security groups that you want to keep after the migration. Because Office 365 won’t migrate these groups, you’ll need to pre-create them in Office 365 so that users will get migrated to them.
Finally, it’s a good idea to reduce the TTL for your MX records to 3,600 seconds, or one hour. Since you’ll be changing these MX records after the migration, reducing the TTL tells other DNS servers to check for updated records more often. This will reduce delays for people who are sending email to your organization immediately after the migration.
Set Up The Migration
To create the migration, log on to the Office 365 admin portal and open the Exchange admin center. Choose More > Migration Endpoints, then click New. For the endpoint type, select Outlook Anywhere. Then, enter the credentials for your migration account. If you have autodiscover enabled, it will be able to figure out your server address from that. Otherwise, enter the external address of your Exchange server. Then, give the migration endpoint a name (anything that makes sense), and click through to complete.
Then, it’s time to set up a migration batch. Back in Exchange admin center, choose Recipients > Migration, then click New > Migrate to Exchange Online. Select the Cutover Migration type, and then confirm the migration endpoint settings that you’ll be using. Then, you’ll be given the option to start the migration immediately, or save it for later. If you’re ready to start migrating, choose the option to start immediately.
Once your migration has completed, it’s time to route mail for your domain to Office 365. Follow the instructions found here to change your MX record to point to Exchange Online mail servers.
Once you’ve confirmed that all your users are connected to their Office 365 mailboxes, and that mail is being routed there successfully, you can delete the migration batch. This will stop mail from being copied from on-prem mailboxes to Office 365, so wait at least 72 hours after changing your DNS records to perform this step.
Also, you can create an autodiscover DNS record that will point your users’ devices to Office 365 automatically. This will simplify their setup of Outlook on personal devices and EAS on phones and tablets. Simply create an alias for autodiscover.yourdomain.com that points to autodiscover.outlook.com