In Kyushu University, Information Infrastructure Initiative provides an email service for students and staff members, called “Primary Mail Service”. We had operated an on-premises system for this service, and the lifetime of this system would end in early 2019. We needed to reduce costs for replacing this system because our university had just finished a major campus migration. We compared some options such as building a yet another on-premise system and migrating to a cloud-based email service and finally gave up the on-premise option because we couldn’t afford replacement and operational costs of another on-premises system anymore. We selected Microsoft Exchange Online as the new service mainly because we already had a contract with Microsoft and been operating an Office 365 tenant. We had additional requirements for user provisioning and services which were not available in Exchange Online, so we had to implement and maintain additional systems on top of it. On December 18th, 2018, we successfully migrated the email service to Exchange Online. By coincidence, Kyushu University Administration Bureau decided to migrate their in-house Exchange server to Exchange Online. After some discussions, they concluded to migrate their domain to the same tenant with Primary Mail Service. Other than that, there are more than a hundred legacy email servers inside our campus network operated by various departments as subdomains of kyushu-u.ac.jp. We are designing a plan to consolidate them into our tenant of Exchange Online to reduce a budget and human resource costs, and to improve security. In this presentation, we share our experiences about migrating our campus-wide email services to Exchange Online. We also discuss why we want to consolidate other legacy email servers and how to implement the plan.