Firstly, Office 365 doesn’t support MBOX file type that is used in Thunderbird for storing mailboxes-comprising emails, attachments, contacts and calendars, etc. However, migrating Thunderbird emails to Office 365 or any other email client along with attachments is not an easy task. Mozilla Thunderbird mail users are migrating to Office 365 for reasons like security, scalability, availability, collaboration, and affordable subscription-based pricing.
