Deciding on the best migration path of your users’ email to Office 365 can be difficult. Your migration performance will vary based on your network, existing messaging systems design, mailbox size, migration speed, and so on.
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.
For migrating third-party email to Office 365, you can configure mail flow coexistence if the third-party email provider permits then migrate the mailboxes using IMAP or cutover migration options.
Migrating from Exchange 2003 or Exchange 2007
Number of mailboxes | How quickly do you want to migrate? | Use |
Fewer than 150 | Over a weekend or a few days. | Cutover |
Fewer than 150 | Slowly, by migrating a few users at a time. | Staged |
Over 150 | Over a weekend or a few days. | Staged |
Over 150 | Slowly, by migrating a few users at a time. | Staged |
Migrating from Exchange 2010 or Exchange 2013 or Exchange 2016 or Exchange 2019
Number of mailboxes | How quickly do you want to migrate? | Use |
Fewer than 150 | Over a weekend or a few days. | Cutover |
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 |
Over 150 | Slowly, by migrating a few users at a time. | Exchange Hybrid |
Migrating from third-party email system to Office 365
Number of mailboxes | How quickly do you want to migrate? | Use |
Fewer than 150 | Over a weekend or a few days. | Cutover |
more than 150 | Slowly, by migrating a few users at a time. | IMAP with mail flow coexistence |
If the mailboxes you’re migrating contain a large amount of data, you can also use Office 365 Import Service to import PST files to Office 365.