In this video the speaker explains how to configure the domain coexistence feature of on-demand migration. The domain coexistence feature allows users in the source Office 365 tenant to start sending email using a new SMTP domain that exists in the target Office 365 tenant before their migration. The speaker demonstrates how to enable domain coexistence in the on-demand migration portal and highlights the changes made to the source and target tenants to support domain coexistence. Also, it explains how to disable the domain coexistence feature if needed.