Major updates are communicated at least 30 days in advance when an action is required and might include:

• Changes to daily productivity such as inbox, meetings, delegations, sharing, and access
• Changes to themes, web parts, and other components that may affect customized features
• Increases or decreases to visible capacity such as storage, number of rules, items, or durations
• Changes to product branding that may: Cause end user confusion,
  Result in changes to help desk processes and reference material, or
  Change a URL
• A new service or application
• Changes requiring an admin action (exclusive of prevent or fix issues)
• Changes to where your data is stored