The best tool to migrate IMAP emails to Office 365 is the IMAP Backup Tool, designed for seamless and secure email migration. This tool allows you to migrate emails from any IMAP-supported email client (such as Gmail, Yahoo, Thunderbird, Zoho, and others) to Office 365 and more without data loss. It ensures a smooth migration by maintaining the folder hierarchy, email formatting, and attachments. Additionally, it supports multiple saving formats like PST, MBOX, EML, MSG, PDF, and HTML, providing flexibility for different email management needs.