When you are planning to migrate email from IBM Lotus Notes to Office 365, use the Microsoft Online Notes Inspector (MONTI) application to evaluate how much data needs to be migrated from a customer's Lotus Notes environment to Office 365.
Here's what MONTI does:
It processes mail files to determine the total database size, document count (calendar, contacts, groups, mail, and tasks), and size by days.
It processes Mail-In Databases to determine the total database size, and Size by Days.
It posts results under the People, Mail-In Databases, and Logs views. You can create these reports manually or on a scheduled basis.
Download the MONTI application and accompanying documentation from the Microsoft Download Center.
The documentation describes how to deploy, configure, and run the MONTI application in a customer’s Domino environment.