Migration from IMAP-enabled email clients to Office 365 admin center is quite a tricky task. The process becomes lengthy and requires some technical skills to accomplish the steps associated while migrating IMAP to Office 365. In this regard, I have recently gone through an informative write-up that explains the detailed stepwise procedure of how to migrate IMAP to Office 365 using the New Exchange Admin Center. This article is really helpful to understand the whole process of migrating the emails from IMAP-supported email clients to the Office 365 admin center. 

Apart from this, it also discusses one more approach which contains the IMAP Mail Backup Tool. This software approach is compatible with both technical and non-technical users. Additionally, it offers to backup and migrates the emails of IMAP-supported email clients into various file formats and email clients. You can also try its free demo version n case you want to analyze its performance.