Step 1: Sign in to Office 365 admin center
Step 2: Navigate to Setup > Data migration
Step 3: Choose Other email sources
Step 4: On the Select your data service page, fill in the appropriate IMAP connection settings(Hostname/IP, port number, email account and password)
Step 5: Click Save
Step 6: Check the box next to the users whose email you want to migrate, and then fill in the email alias, and the password
Step 7: Choose Start Migration