Outlook on iPhone won't sync with PC

Hello @杉山 明宏

Thank you for reaching out to the Microsoft Q&A forum.

Based on the information you shared, I understand that you are experiencing an issue where Outlook on your iPhone is not syncing sent and received emails correctly. You mentioned that this issue first occurred when your mailbox reached its maximum storage limit, and even after extending the storage, the problem has not yet been resolved.

To help refresh the connection and resync your mailbox, please try resetting your account in the Outlook app on your iPhone by following the steps below:

1. Open the Outlook app on your iPhone.
2. Tap Settings.
3. Scroll down and, under the General section, select Accounts.

4. Choose the account that is experiencing the issue.
5. Scroll to the bottom and tap Reset Account.

After completing these steps, please allow a few minutes for the mailbox to resync. Then, check whether your emails are now sending, receiving, and syncing correctly.

Kindly let me know the outcome after trying the steps above, and I will be happy to assist you further if needed. I look forward to hearing from you.

The mailbox storage issue is already fixed on the server side (email works on the PC), so the problem is now limited to the iPhone’s connection/sync partnership with the mailbox.

Follow these steps in order:

1. Confirm the account itself is healthy
   • Because storage was previously exceeded, verify the mailbox is now below quota and fully usable:
     • From a browser, sign in to Outlook on the web or Outlook.com (depending on the service used by the company) and confirm new mail can be sent and received there.
   • If using Outlook.com, also confirm Microsoft cloud storage is not full, because a full cloud storage prevents sending/receiving mail at all. See the storage check described in Can't send or receive email in Outlook.com.
2. Remove the existing mobile device partnership from the mailbox When a device stops syncing after a quota or server issue, removing the old device partnership and letting it recreate often fixes the problem. For Outlook.com or Outlook on the web:
   1. In a browser, sign in to the mailbox.
   2. Go to Settings > General > Mobile devices.
   3. In the list of devices, select the iPhone entry.
   4. Delete the device partnership.
   5. Select Save at the top.
   This does not wipe the phone; it only removes the sync relationship for email.
3. Power-cycle the iPhone and resync
   1. Completely power off the iPhone.
   2. Turn it back on after a few seconds.
   3. Open Outlook for iOS and allow it to resync with the mailbox.
   If Outlook for iOS still does not sync, remove the account from the Outlook app and add it again after the partnership has been removed in step 2.
4. If the account was added as IMAP/POP on the phone
   • If the email profile on the iPhone was configured as IMAP or POP instead of Exchange/Exchange ActiveSync, calendar and contacts will not sync, and mail sync can behave differently from the PC.
   • Ensure the account is added in Outlook for iOS as a Microsoft 365 or Exchange account (Exchange ActiveSync) rather than IMAP/POP. See the guidance under Can't sync calendar and contacts after set up in the Outlook mobile troubleshooting article.
5. If issues persist
   • For a Microsoft 365 work or school account, contact the organization’s Microsoft 365 admin or technical support so they can:
     • Confirm the mobile device is allowed by any mobile device mailbox policies.
     • Check for any blocks or quarantine on the device.
     • Review server-side logs for sync errors.

References:

• Troubleshoot Outlook mobile issues
• Fix email sync issues by removing a device from your Outlook mailbox
• Can't send or receive email in Outlook.com