Hi SumnerDa, If you use Exchange to connect your account to any client, mails, contacts and calendars in this account always sync between these devices. If you want to migrate contacts from other accounts to Office 365: Use iCloud to sync iPhone contacts to your Apple account and then export iCloud contacts on Outlook for Mac. Since Outlook only supports a single vcard, you can import them into gmail and then export in the Outlook format (CSV). If you want to migrate calendars from other accounts to Office 365: Export calendars to ics files and then import them to Office 365 Import or subscribe to a calendar in Outlook.com or Outlook on the web For mails, you can set your iCloud mailbox and Office 365 account in Outlook for Mac and then export mails to an archive file.
After that, import that file to your Office 365 account via Outlook for Mac: Export items to an archive file in Outlook for Mac Import email messages, contacts, and other items to Outlook 2016 for Mac Thanks, Alison.