Calendar events were unexpectedly deleted after sync issue

Hi 凱琳 凱琳,

Welcome to Microsoft Q&A forum. 

I understand how inconvenient it is when reminders/events in your Hotmail/Outlook.com calendar suddenly disappear after syncing with another app.

For Outlook.com, you can try these self-service recovery steps first:

• Sign in to Outlook on the web (Outlook.com) > switch to Mail > open the Deleted Items folder.
• Look for calendar items (appointments/meetings) and move/restore them back to Calendar.
• If you don’t see them in Deleted Items:
  • While still in Deleted Items, select “Recover items deleted from this folder”, then choose the calendar items and click Restore.

Note: If the reminders/events were created in a third‑party app and were not successfully synced/uploaded to Outlook.com, they may not appear in Outlook.com’s recovery folders.

If you’ve checked both Deleted Items and “Recover items deleted from this folder” and still cannot find the missing items, please note this is a user-to-user support forum. Moderators and contributors don’t have access to back-end systems or the ability to perform “backend recovery,” so the next best step is to contact Microsoft Support for Outlook.com.

• Go to Contact Us: https://support.microsoft.com/en-us/contactus
• Click Show expanded list of products
• Select Outlook > Get Home support
• Type Outlook live chat in the search box, then select Get Help > Contact Support
• If you can’t sign in to the affected account, sign in with a different Microsoft account to access support options
• Under Products & Services, select Other Products > Outlook, then choose Chat with a support agent via web browser

Thank you for your understanding. 

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread. 

Backend recovery options for deleted Outlook.com (Hotmail) calendar items are not described in the provided information. The available context only covers how to sync Outlook calendars with mobile apps, how to troubleshoot general sync issues, and where to get additional Outlook help.

For this scenario, the only supported next step in the context is to contact Microsoft support directly and provide full details (account type, affected calendar, approximate deletion time, and apps involved) so they can investigate whether recovery is possible on the service side.

To proceed:

1. Go to Microsoft support and open a support request for Outlook.com calendar data loss.
2. If this is a work or school account, also contact the Microsoft 365 admin or technical support for the tenant.
3. If using Outlook mobile, you can additionally use the in-app support channel to report the calendar deletion and sync issue.

References:

• Can't sync calendar and contacts with my phone or tablet