Mail on Mac not syncing with 365

Question

Hello

I am using Apple mail as email client, my mail [Moderator note: personal info removed] stopped syncing though the account looks fine and online

I tried to rebuild the mailbox yet no new mails are coming since last sunday

on a separate note I checked the mailbox is 30% full

so please advice

Answer 1

If your Apple Mail is not syncing with your Microsoft 365 account, here are some steps you can take to troubleshoot the issue:

1. Verify Internet Connection: Ensure your device has a stable internet connection.
2. Check Account Settings: Confirm that your email account settings in Apple Mail are correct, including the incoming and outgoing server settings as specified by Microsoft 365.
3. Rebuild Mailbox: Since you mentioned you have already attempted to rebuild the mailbox, ensure that the process was completed correctly, as it may take some time for the mailbox to fully rebuild.
4. Update Software: Make sure that both your macOS and Apple Mail application are updated to the latest versions, as outdated software can lead to syncing problems.
5. Monitor Service Status: Check the Microsoft 365 Service health status to see if there are any ongoing issues that might be affecting email delivery.
6. Remove and Re-add Account: If the problem persists, consider removing your email account from Apple Mail and then re-adding it. This can often resolve syncing issues.

If these steps do not resolve the issue, you may want to reach out to Microsoft support for additional help.

Answer 2

I tried all but still not working

Answer 3

Hi Hussein Delawar,

Thank you for posting your question in the Microsoft Q&A forum. 

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

I understand you’ve already tried several troubleshooting steps, your mailbox is only 30% full, yet Apple Mail has stopped syncing. Based on what you’ve shared, here are a few additional, targeted checks to help isolate and resolve the issue.

1) Verify server-side mail state via Outlook on the web (OWA)

Before changing anything on the Mac, please sign in to Outlook on the web with the same account and confirm that new emails are present there. If OWA shows all recent mail: the service is healthy and the problem is local to the Mac client. Proceed to step 2.

2) Clear macOS Keychain Access credentials used by Exchange/Microsoft 365

This resets the local authentication tokens/passwords that Apple Mail and Office apps use.

1. Quit all Office apps and Mail app.
2. Open Keychain Access (Spotlight > type Keychain Access).
3. In Keychain Access, select the login keychain. From the View menu, choose Show Invisible Items.
4. Use the search box (top right) and delete entries that match the following keys for your account:
   • adal > delete items of kind MicrosoftOffice15_2_Data:ADAL:<GUID>.
     These are Modern Authentication tokens.
   • office > delete Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2 (Outlook v15.x), or Microsoft Office Identities Cache 3, Microsoft Office Identities Settings 3, Microsoft Office Ticket Cache (Outlook v16.x/New Outlook).
5. Restart the Mac.
6. Open Mail and sign in again. If macOS prompts for Keychain access, choose "Always Allow".

Notes: Removing ADAL/Office Identities will also sign you out of other Office apps on the Mac; this is expected and helps remove duplicate or stale tokens.

3) Organization & connectivity checks (optional but recommended)

• Ask your administrator whether other users in your organization are experiencing similar sync issues. If yes, review Service health for Exchange Online.
• Try another network (e.g., mobile hotspot) to rule out a local firewall/proxy that could be interrupting Autodiscover/EWS or IMAP/SMTP flows.

I hope the suggestions above helpful.

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