Multiple events missing from Outlook calendar across multiple platforms

Calendar items that appear missing across all clients (Outlook on the web, Outlook app, iPhone Mail, etc.) are typically either:

1. Outside the sync display range of a given client, or
2. A result of a broader calendar data issue that must be handled by Microsoft support.

From the provided information, the following points are relevant:

1. Calendar apps (including Mail and Calendar for Windows 10, and mobile apps) do not always show the full historical range of events:
   • On PCs, Exchange ActiveSync accounts (Outlook.com / Hotmail / Microsoft 365) show events from the past 3 months and all future events.
   • On mobile devices, Exchange ActiveSync accounts show events from the past 2 weeks and all future events.
   • Older events are not deleted; they simply are not displayed in those apps and can still be viewed via the web or another client.
   However, in this scenario, events are missing even when checking via the desktop/web, so this is not just a display-range limitation.
2. When calendar items are missing and not found in Deleted Items or Recover Deleted Items, standard Outlook troubleshooting focuses on:
   • Ensuring the Outlook client is fully updated.
   • Using supported versions of Outlook.
   • Verifying that Deleted Items Recovery is enabled and using it to recover deleted items when possible.
   Since the events are not present in Deleted Items or Recover Deleted Items, and they are gone across all platforms, this indicates the items are not simply hidden by a client-side issue.
3. For issues where calendar data is missing or out of sync between devices and the mailbox (for example, with Exchange ActiveSync), the recommended approach is to:
   • Remove and re-create the ActiveSync relationship on the device.
   • Remove the device partnership from Outlook on the web (Settings → Options → Phone → Mobile Devices → Delete the device relationship) and then re-add the account.
   In this case, the user has already removed and re-added the account on the iPhone, and the items are missing even in the mailbox viewed via the desktop/web, so this is not just a device-sync corruption issue.

Given the constraints of the available information, there is no documented, user-accessible way in this context to restore an Outlook.com/Hotmail calendar “from Microsoft’s side” (for example, restoring a point-in-time snapshot of the entire calendar) beyond the standard Deleted Items / Recover Deleted Items mechanisms and client troubleshooting. When items are missing across all platforms and not present in Deleted Items or Recover Deleted Items, the next step is to engage Microsoft support directly so they can investigate at the service level.

Summary of actionable steps based on the context:

1. Confirm display range is not the cause
   • On each client, ensure the view includes the dates in question.
   • Be aware that some apps only show a limited past range (e.g., 2 weeks or 3 months), but the web mailbox should show the full range if the items still exist.
2. Verify standard recovery paths
   • Check Deleted Items and use Recover Deleted Items in Outlook/Outlook on the web to see if any of the missing appointments can be restored.
3. Ensure clients are supported and updated
   • Use a supported, fully updated Outlook client when checking the calendar.
4. If items are still missing everywhere
   • Contact Microsoft support (for Outlook.com/Hotmail) so they can check the mailbox at the service level. The context provided does not describe a self-service method to restore an entire Outlook.com calendar from a previous point in time.

References:

• Where are my email messages or calendar events in Mail and Calendar for Windows 10?
• How to troubleshoot missing and duplicate appointments in Outlook
• Calendar on mobile device isn't synced to the calendar in an Exchange Online mailbox when you use Exchange ActiveSync