You have different migration methods available if you want to
Migrate Exchange On Premise to Exchange Online.
Cutover migration – a classic approach to migration. Exchange 2013 is the last on-premises Exchange version that allows this type of mailbox move. In short, it allows you to move all mailbox content in one hop. It cannot be performed if you have more than 2000 mailboxes, but as this Microsoft’s article suggests, “due to length of time it takes to create and migrate 2000 users, it is more reasonable to migrate 150 users or fewer.”
Hybrid migration – a hybrid migration means that you create and configure an environment with both on-premises Exchange server and Exchange Online (using the Hybrid Configuration Wizard) and move content from on-prem mailboxes to remote mailboxes in the cloud. While this gives you more freedom in staging the migration, it makes your IT infrastructure a bit more complicated. In short, you manage mailboxes on-premises, but all the changes are synced to the cloud using Azure AD Connect. Most people don’t entirely understand how hybrid environments work.
Although Exchange 2013 allows you to configure a hybrid environment, it might be an idea worth reconsidering. Creating an Exchange 2013 and Exchange Online hybrid just before the server’s end of life leaves you with a considerable security risk. More reasonable would be to migrate to Exchange 2019 first and then, configure hybrid. That’s, however, twice as much work and twice as many opportunities for things to go wrong.
Express migration – also called Minimal Hybrid. It’s a hybrid migration minus directory synchronization. It is supposed to be the quickest native migration method available.
Manual methods – usually include recreating your organization’s structure in the cloud and using PST files to migrate content. That means exporting PST files on the source server (you can make it much easier if you use PowerShell, as I described here) and importing them to the target environment. Due to a lot of heavy lifting, the fragility of PST files and multiple levels on which it can go wrong, it is not recommended. Still, if you have only a few mailboxes and a backup in place, this might just work.
Third party tools – use different methods to make the move smoother, quicker and easier. They are especially useful when migrating big environments with hundreds or thousands of mailboxes.
Why use a third-party tool for migration? You don’t need to use a third-party tool to migrate from Exchange 2013 to Microsoft 365. However, using migration software, like Apps4Rent Office 365 Migration, is the easiest way to go full cloud or go hybrid with least effort. Migration is a challenging task, that’s why more and more administrators seek for help in taking the burden off their shoulders.