Here is a step by step guide to connecting your Office 365 email address with FUB when you have two factor authentication enabled (you require a pin code to login).
You will need to acquire an "app password" to connect your email address with FUB.
1. Login at https://login.microsoftonline.com
2. Then go to Office 365 settings, by clicking the cogwheel icon at the top and then clicking the "Office 365" link at the bottom.
3. Then click "Security & privacy" section on the left and click the "Additional security verification" section, then click the "Update your phone numbers used for account security".
4. Click the "App Passwords" link (it doesn't look like a link)
5. Click the "create" button to create a new app password
6. Name it "followupboss" for reference
7. Use the password it generated to connect your email with FUB.
8. In the FUB settings screen, click the "other provider" link
9. Choose "Connect Your Office 365 Email"
10. Place the app password from step 7 where it asks for your Office 365 password. It should now connect.