There are various tools available for the users to migrate mailboxes from source IMAP to office365 server. But, I recommend EdMails IMAP to office 365 Software particularly designed to work in multiple domains and allows the users to migrate IMAP to office365/ Exchange server effortlessly. The tool compatible with all IMAP email servers like Google mail - Gmail, Outlook.com, Office365.com, Yahoo Mail, Yahoo Mail Plus, Yahoo Mail UK, Yahoo Mail, Etc., both technical and non-technical can easily access this tool without any technical skill. The tool is well developed with some amazing features which can efficiently migrate all IMAP emails to office365. Competitor 

Software features:-
•    Simple and user friendly Tool.
•    Migrate emails from all IMAP servers to Office 365 or Exchange Server.
•    Automatic mailbox mapping between IMAP to O365/ Exchange server.
•    Supports specific folders or emails migration from source IMAP to target server.
•    Supports incremental migration to avoid duplicate items migrations to the target server
•    Automatic mailbox mapping to the destination server.
•    Migration includes personal, archive, shared and public folders.

Know More: IMAP migration