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# Troubleshooting Calendar Not Syncing in Outlook or Mobile

> Resolve calendar sync failures in Outlook and on mobile by checking Exchange connectivity, permissions, and account configuration step by step.

Calendar sync failures can appear as missing appointments, events that do not update after changes, or a mobile device that stops reflecting calendar entries entirely. The most common causes are a disrupted Exchange or Microsoft 365 connection, an account that needs to be re-added on a mobile device, stale cached data, or insufficient permissions on a shared calendar. Work through each section below in sequence until your calendar is syncing correctly.

<Note>
  These steps cover Microsoft 365, Exchange Online, and Exchange On-Premises environments. If your organization uses Google Workspace, the account re-addition steps and connectivity checks still apply, but the specific settings will differ.
</Note>

## 1. Check Exchange / Microsoft 365 Connectivity in Outlook

Before investigating device or account-specific settings, confirm that Outlook itself has a healthy connection to the mail server.

<Steps>
  <Step title="Check the connection status indicator">
    Look at the bottom status bar of the Outlook window. It should read **Connected to: Microsoft Exchange** or **Connected**. If it shows **Disconnected**, **Trying to connect**, or **Working Offline**, your connection to the server is interrupted.
  </Step>

  <Step title="Disable Work Offline mode">
    Click **Send/Receive** in the ribbon and check whether **Work Offline** is highlighted (active). If it is, click it to toggle it off and reconnect.
  </Step>

  <Step title="Run Microsoft Support and Recovery Assistant">
    For Microsoft 365 accounts, Microsoft's official diagnostic tool can detect and fix connectivity and sync issues automatically:

    ```text theme={null}
    # Download from Microsoft
    https://aka.ms/SaRA-OutlookSetup
    ```

    Run the tool and follow the prompts to diagnose your Outlook profile.
  </Step>

  <Step title="Check Microsoft 365 service health">
    Visit the Microsoft 365 Service Health Dashboard or ask your administrator to check it. A widespread Exchange Online outage will affect all users and cannot be resolved locally:

    ```text theme={null}
    https://status.office365.com
    ```
  </Step>

  <Step title="Test Exchange connectivity with Outlook's built-in tool">
    Hold **Ctrl** and right-click the Outlook icon in the system tray, then select **Test E-mail AutoConfiguration**. Enter your email address, uncheck **Use Guessmart** and **Secure Guessmart Authentication**, then click **Test**. Review the **Results** tab for any errors in the Autodiscover or Exchange connectivity process.
  </Step>
</Steps>

<Tip>
  If the AutoConfiguration test shows an Autodiscover failure, your IT administrator may need to verify the Autodiscover DNS record or internal Exchange URL configuration.
</Tip>

***

## 2. Force a Calendar Sync in Outlook

Sometimes the Outlook client simply needs a nudge to pull the latest calendar data from the server.

<Steps>
  <Step title="Trigger a full Send/Receive cycle">
    Press **F9** or click **Send/Receive → Send/Receive All Folders**. This forces Outlook to synchronize all folders, including Calendar, with the server.
  </Step>

  <Step title="Manually sync the Calendar folder">
    In the folder list on the left, right-click your **Calendar** folder and select **Properties**. Under the **Synchronization** tab (available for Exchange accounts), click **Clear Offline Items**, then click **OK**. Outlook will re-download all calendar data from the server.
  </Step>

  <Step title="Rebuild the local OST cache">
    If the above does not resolve the issue, close Outlook and navigate to:

    ```text theme={null}
    C:\Users\<YourUsername>\AppData\Local\Microsoft\Outlook\
    ```

    Rename your `.ost` file (e.g., append `.old` to the filename) rather than deleting it. Outlook will create a fresh OST file and re-sync all data — including your calendar — from the server on next launch.
  </Step>
</Steps>

<Warning>
  Renaming the OST file triggers a full re-download of your mailbox. This can take several minutes to hours depending on mailbox size and connection speed. Do not perform this step immediately before a meeting or deadline.
</Warning>

***

## 3. Fix Calendar Sync on a Mobile Device

Mobile calendar sync issues are most often caused by an account in an error state. The fastest resolution is to remove and re-add the account.

<Steps>
  <Step title="Check the sync error notification">
    On **iOS**: Go to **Settings → Mail → Accounts**, tap your Exchange or Microsoft 365 account, and look for a warning icon or error message. On **Android**: Go to **Settings → Accounts**, select your account, and check for a sync error badge.
  </Step>

  <Step title="Force a manual sync">
    On **iOS**: Open the Calendar app, pull down on the calendar view to trigger a refresh. On **Android**: Open **Settings → Accounts → \[Your Account] → Sync Now**.
  </Step>

  <Step title="Toggle calendar sync off and on">
    On **iOS**: Go to **Settings → Mail → Accounts → \[Your Account]** and toggle **Calendars** off, wait 10 seconds, then toggle it back on. On **Android**: Go to **Settings → Accounts → \[Your Account]** and uncheck then re-check **Sync Calendar**.
  </Step>

  <Step title="Remove and re-add the account">
    If toggling sync did not help, remove the account entirely and add it back fresh:

    **iOS:**

    1. Go to **Settings → Mail → Accounts → \[Your Account] → Delete Account**.
    2. Return to **Accounts → Add Account → Microsoft Exchange**.
    3. Enter your email address and tap **Next**. Sign in with your credentials when prompted.
    4. Ensure **Calendars** is enabled and tap **Save**.

    **Android (Outlook app):**

    1. Open the Outlook app, tap your profile picture, then **Settings → \[Your Account] → Delete Account**.
    2. Re-add the account via **Settings → Add Account → Add Email Account**.
  </Step>

  <Step title="Check the Exchange server address (legacy ActiveSync)">
    If you are using the native iOS/Android mail app with ActiveSync rather than the Outlook app, ensure the Exchange server address is correct:

    ```text theme={null}
    # Microsoft 365
    outlook.office365.com

    # Exchange On-Premises (ask your IT administrator for the exact address)
    mail.yourdomain.com
    ```
  </Step>
</Steps>

<Note>
  The Outlook mobile app (iOS and Android) is generally more reliable for Microsoft 365 and Exchange calendar sync than the built-in device mail clients. If you continue to experience issues with the native mail app, try switching to the Outlook app.
</Note>

***

## 4. Check Shared Calendar Permissions

If a shared calendar (a colleague's calendar, a room calendar, or a team calendar) is not showing or not updating, the issue is likely a permissions problem rather than a connectivity problem.

<Steps>
  <Step title="Verify your permission level">
    Ask the calendar owner to confirm your access level. In Outlook, the owner can check by right-clicking the calendar, selecting **Properties → Permissions**, and reviewing your entry. The minimum required for basic viewing is **Reviewer**.
  </Step>

  <Step title="Re-accept the sharing invitation">
    Ask the calendar owner to resend the sharing invitation. Open the invitation email and click **Open this Calendar** (or **Accept**). This refreshes the permission link on your client.
  </Step>

  <Step title="Remove and re-add the shared calendar">
    In Outlook, right-click the shared calendar in the folder list and select **Delete Calendar**. Then re-add it:

    1. Go to **Home → Open Calendar → Open Shared Calendar**.
    2. Type the name or email address of the calendar owner and click **OK**.
  </Step>

  <Step title="Check calendar overlay mode">
    If the shared calendar appears in your list but events are not visible, ensure it is not toggled off. Click the calendar name's checkbox in the **My Calendars** or **Other People's Calendars** panel to ensure it is enabled (coloured, not greyed out).
  </Step>

  <Step title="Verify Microsoft 365 admin permissions (for admins)">
    For administrators, verify calendar delegation using PowerShell:

    ```powershell theme={null}
    # Check mailbox folder permissions for a calendar
    Get-MailboxFolderPermission -Identity "owner@domain.com:\Calendar"
    ```
  </Step>
</Steps>

<Tip>
  Default calendar sharing in Microsoft 365 allows users to share their calendar with permission levels ranging from **Free/Busy only** to **Full Details** to **Can edit**. If a user can see events but not their details, they likely only have Free/Busy access — ask the owner to increase the permission level.
</Tip>

***

## Escalation

<Accordion title="When to escalate to your IT Help Desk">
  Escalate if any of the following apply after completing all steps above:

  * The Outlook AutoConfiguration test shows Autodiscover failures that persist after reconnecting, indicating a DNS or Exchange configuration problem.
  * Multiple users in your organization are experiencing calendar sync failures simultaneously — this suggests a server-side or Exchange/Microsoft 365 issue.
  * Re-adding the account on mobile fails at the sign-in step, which may indicate a Conditional Access policy, MFA configuration, or licensing problem.
  * Calendar events from a specific date range are permanently missing after an OST rebuild, which may require mailbox recovery.
  * Shared calendar permissions appear correctly configured but sync still fails — this can indicate a broken calendar delegation object that must be repaired by an Exchange administrator.

  When logging a ticket, include:

  * Whether the issue affects your own calendar, a shared calendar, or both.
  * The devices and Outlook versions affected.
  * The error message shown in the mobile account settings, if any.
  * The results of the Outlook AutoConfiguration test (screenshot of the Results tab).
</Accordion>