Office 365 - Handling locally stored data from your client during the transition
If you use a desktop email / calendar client -- such as Outlook, Apple Mail, or Thunderbird -- you may want to continue to use some of the data that your email client is storing on your computer after your account is moved to Office 365. The steps that you will need to take to continue using this content will vary, depending on what client you currently use and what client you plan to use after your transition to Office 365. Answer the questions below for a recommendation.
Note: Please use discretion when deciding whether to move locally stored content. In some cases, it may be possible to export content from your current client, but there may be no viable option for importing the content into your new client.
What client are you currently using to access your email and calendar?
Outlook 2013 (Windows)
Apple Mail / Calendar / Contacts / Reminders