Based on your survey responses, we recommend that you set up Office 365 mail services using a Simple MRS Proxy mailbox migration. ...

Based on your survey responses, we recommend that you set up Office 365 mail services using a Simple MRS Proxy mailbox migration.  A Simple MRS Proxy migration is similar to an Exchange hybrid deployment in that mailboxes are moved from an on-premises Exchange 2010 or Exchange 2013 organization to Office 365 using the Mailbox Replication Proxy Service (MRSProxy).  Like an Exchange cutover migration, a Simple MRS Proxy is intended for Exchange organizations that want to have cloud-only IDs for their Office 365 users. However, unlike a cutover migration, it does not have a 2,000-mailbox migration limit and you can migrate Exchange Archive mailboxes.