You can migrate the contents of user mailboxes to %BRAND_OFFICE_365_SHORT% when your current email system supports the Internet ...

You can migrate the contents of user mailboxes to %BRAND_OFFICE_365_SHORT% when your current email system supports the Internet Message Access Protocol — better known as IMAP. Contacts and calendar items are not migrated during an IMAP migration, but we include additional steps to help you import contacts and calendars into %BRAND_OFFICE_365_SHORT%.