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Decide on a migration path in Exchange Online

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Deciding on the best migration path of your users' email to Microsoft 365 or Office 365 can be difficult. This article gives guidance based on your current email system and other factors, such as how quickly you want to migrate to Microsoft 365 or Office 365. Your migration performance will vary based on your network, mailbox size, migration speed, and so on.

Important

This topic is intended for administrators. If you want to migrate email for a single account, see Migrate email and contacts to Microsoft 365 or Office 365 instead.

How do I decide which method to use?

Before you start an email migration, review the limits and Migration performance and best practices for Exchange Online to make sure you get the performance and behavior you expect after migration.

You can migrate mailboxes from an Exchange Server or from another email system. The content in the following sections is organized by email system, and the linked topics help you decide on the best method based on number of mailboxes and your time and mailbox size constraints.

Your existing system is an Exchange Server

For migrations from an existing on-premises Exchange Server environment, you can migrate all email, calendar items, tasks and contacts from user mailboxes to Office 365. The available methods are cutover, staged, and Exchange Hybrid migrations. These migration methods copy over all mail data, including contacts, calendar items, and tasks. You can also use the Internet Message Access Protocol (IMAP) migration from Exchange servers, and if your Exchange server is older than Exchange 2003, IMAP migration is your only option. Note that IMAP migration will copy over only email data.

Important

Staged and Exchange Hybrid migrations require that you also set up directory synchronization. For more information, see Microsoft 365 or Office 365 integration with on-premises environments.

For migration recommendations, expand one of the following sections based on your source system:

Exchange 2003 or Exchange 2007

If your source system is Exchange 2003 or Exchange 2007, consider the following options.

Note

Even though cutover migration supports moving up to 2000 mailboxes, due to length of time it takes to create and migrate 2000 users, it is more reasonable to migrate 150 users or less.

Number of mailboxes How quickly do you want to migrate? Use
Fewer than 150 Over a weekend or a few days. Cutover
For an overview, see What you need to know about a cutover email migration to Microsoft 365 or Office 365.
Fewer than 150 Slowly, by migrating a few users at a time. Staged
For an overview, see What you need to know about a staged email migration.
Over 150 Over a weekend or a few days. Staged
If you have more than 150 mailboxes , the best method is to use staged migration where you can migrate a limited number of users at a time. This is because cutover migration performance suffers when you try to migrate more than 150 mailboxes.
Over 150 Slowly, by migrating a few users at a time. Staged

If the mailboxes you're migrating contain a large amount of data, you can also use the Import service to import PST files to Microsoft 365 or Office 365. You can use the Microsoft 365 or Office 365 Import Service to either ship the files or to import them across the network.

If you have an extremely large number of mailboxes (5,000+), you might want to hire a partner to help you migrate your email data.

You can search for partners on the Microsoft solution providers page.

Exchange 2010, 2013 or 2016

If your source system is Exchange 2010, Exchange 2013 , or Exchange Server 2016, consider the following options.

Note

Even though cutover migration support moving up to 2000 mailboxes, due to length of time it takes to create and migrate 2000 users, it is more reasonable to migrate 150 users or less.

Number of mailboxes How quickly do you want to migrate? Use
Fewer than 150 Over a weekend or a few days. Cutover or Express migration.
Fewer than 150 Slowly, by migrating a few users at a time. Exchange Hybrid
Over 150 Over a weekend or a few days. Exchange Hybrid
If you have more than 150 mailboxes, the best method is to use an Exchange hybrid migration where you can migrate a limited number of users at a time. This is because cutover migration performance suffers when you try to migrate more than 150 mailboxes.
Over 150 Slowly, by migrating a few users at a time. Exchange Hybrid

If the mailboxes you're migrating contain a large amount of data, you can also use the Import service to import PST files to Microsoft 365 or Office 365. You can use the Import Service to either ship the files or to import them across the network.

If you have an extremely large number of mailboxes (5,000+), you might want to hire a partner to help you migrate your email data.

You can search for partners on the Microsoft solution providers page.

Exchange Server 2000 or earlier versions

For earlier versions of Exchange server, you will have to use IMAP migration.

Other email systems

For other email systems that support IMAP, you can use IMAP migrations.

Depending on your source system, see one of the following:

If the mailboxes you're migrating contain a large amount of data, you can also use the Import service to import PST files to Microsoft 365 or Office 365. You can use the Import Service to either ship the files or to import them across the network.

You can also hire a partner to help you migrate your email data. You can search for partners on the Microsoft solution providers page.

Leave us a comment

Were these instructions helpful? If so, please let us know at the bottom of this topic. If they weren't, and you're still having trouble deciding on a migration strategy, tell us what source email system you want to migrate from and we'll use your feedback to improve our content.