Outlook mobile not syncing all event from outlook on my desktop

Hi @Rob Hudson, 

I hope you are doing well today. 

Based on the information you shared that some calendar events created in Outlook on your desktop are not appearing in Outlook on your mobile device. 

Regarding your concern, some calendar events on your Outlook Desktop are not appearing on your Outlook iOS mobile application. This typically occurs because the calendar sync period on your mobile app may be set to a limited timeframe, which means events outside of that window will not be displayed. Furthermore, certain events may be stored in a secondary or local calendar folder on your desktop that has not been enabled on your mobile device. In some cases, the account connection on your mobile app may also require a refresh in order to fully reflect the latest changes from your desktop. 

To get everything back on track, please follow the three steps below carefully, in order. 

1/ Adjust your mobile sync period 

• Open Outlook on your iPhone and tap your Profile Icon in the top-left corner. 
• Go to Settings > tap your Email Account > select Sync Calendar. 
• Change the sync period to 3 Months or All Events to make sure all events are included. 

2/ Check that all calendars are enabled on mobile 

• In the Outlook iOS app, tap the Calendar icon at the bottom, then tap the Menu (☰) in the top-left. 
• Review the list of calendars and make sure every calendar you use on Desktop, including shared or delegated calendars, has a checkmark next to it. 
• If any calendar is unchecked, tap it to enable visibility. 

3/ Check Your Account Settings

• Go to "Settings" on your iPhone. 
• Scroll down and select "Passwords & Accounts." 
• Select your Outlook account and ensure that the "Calendars" toggle is enabled. 

4/ Check calendar sync settings

Ensure that your Outlook calendar is set to sync with your iPhone. To check this: 

• Go to "Settings." 
• Scroll down and select "Calendar." 
• Under the "Accounts" section, check that your Outlook account is listed, and the "Calendars" toggle is enabled. 

5/ Remove and re-add your account on iOS 

• If the above steps do not bring the missing events through, go to Settings > tap your Account > select Delete Account. 
• Once removed, tap Add Email Account and sign back in with your Microsoft credentials. 
• This will perform a full, fresh sync between your mobile app and your Microsoft 365 mailbox. 

6/ Contact IT administrator:    

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.         

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn    

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.        

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.          

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

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Use the following checks and steps to resolve Outlook desktop events not syncing to Outlook mobile:

1. Verify the account type

• On the desktop Outlook where events are created, confirm the mailbox is an Exchange or Outlook.com account.
• If the account is configured as IMAP or POP, calendar items do not sync to mobile. In that case, the account must be added as an Exchange/Outlook.com (Exchange ActiveSync) account instead.

2. Confirm the calendar is enabled in Outlook mobile

• Open the Outlook mobile app.
• Go to Calendar.
• Tap the three lines (≡) in the upper left.
• Under the email accounts list, ensure the relevant account has Calendar checked.
• If the email address is not listed there, the account is not set up using Exchange ActiveSync; remove and re-add it without using IMAP.

3. Check app permissions on the phone

• iOS: Open Settings > scroll to Outlook > ensure Contacts and Background App Refresh are turned on.
• Android: Open Settings > Applications > Outlook > ensure Contacts is enabled. Then open Outlook > Settings > tap the account > turn on Sync Contacts.

4. Reset the account in Outlook mobile

• In Outlook mobile, go to Settings.
• Tap the account that is not syncing.
• Tap Reset Account and wait for resync.

5. Remove and re-add the account in Outlook mobile

• In Outlook mobile, go to Settings.
• Tap the affected account > Delete Account > Delete From This Device.
• Add the account again using the Exchange/Outlook.com option (do not choose IMAP/POP). If prompted for server settings, obtain the correct Exchange/Outlook.com settings from the mail provider.

6. Validate sync via Outlook on a PC

• On a Windows PC, configure the same mailbox in Outlook using the Exchange protocol.
• Send a test email and create a test calendar event.
• Close Outlook, restart the PC, reopen Outlook, and confirm the test event appears.
• Check Outlook mobile again to see if the test event and other events now sync.
• If the event still does not appear, open Outlook mobile, go to Settings, and restart the app.

7. If the account previously synced and then stopped

• If this is an Outlook.com or Microsoft 365 work/school account that used to sync and now does not, review the guidance in Fix Outlook.com email sync issues (linked from the troubleshooting article) and, if needed, remove and re-create the device partnership from Outlook on the web.

If the mailbox works correctly on desktop/Outlook on the web and all steps above are completed, the issue is likely with the mobile app or device; reinstalling Outlook mobile or contacting support for the specific device may be required.

References:

• Can't sync calendar and contacts with my phone or tablet
• Troubleshoot Outlook mobile issues
• Sync basics - what you can and cannot sync