Outlook Not Syncing on a Mac? How to Fix It

When Outlook on a Mac stops syncing, it can affect your email, calendar, contacts and shared mailboxes. Usually the cause is the connection, Outlook’s stored copy of the mailbox or the account setup, and you can fix it without reinstalling anything. This guide starts with a change from October 2026 that may be the answer, then goes through the usual fixes.

First, check which Outlook you are using

From October 2026, the older version of Outlook for Mac, which Microsoft calls legacy Outlook, stops working against Exchange Online mailboxes. That covers Microsoft 365 business mailboxes. Legacy Outlook used an older connection method, Exchange Web Services, and Microsoft’s published date for retiring it is 1 October 2026.

If you still use legacy Outlook, this is likely why it stopped syncing. To switch, open Outlook and turn off the Legacy Outlook switch. If you do not see the switch, choose Help, then Check for Updates, to get the newer version, or download it from the App Store.

Microsoft says legacy Outlook for Mac keeps working against Exchange on-premises mailboxes until 9 October 2029. Accounts added in one version are not added automatically to the other, so check your accounts after you switch.

What a sync problem looks like

New emails stop arriving, sent messages do not show on other devices, calendar changes are missing or shared mailboxes look out of date.

A simple test is to open Outlook on the web in a browser. If everything is correct there but not on your Mac, the problem is with the Outlook app, not your account.

Restart your Mac

Restart first. It clears stuck background processes and temporary network problems. Open Outlook again and see whether syncing resumes.

Check that Outlook is not working offline

If Work Offline is turned on, Outlook stops sending and receiving. Check the Outlook menu and turn it off.

Check the account is connected

Outlook can look normal while the account behind it is disconnected. Choose Tools, then Accounts, and look at the connection status for the account. Then check the mailbox in Outlook on the web.

Update Outlook

An old version of Outlook can cause sync problems. Open Outlook, choose Help, then Check for Updates, and install everything available. Several sync problems have been fixed in later builds. Intermittent sync problems have also been under investigation, so a fix may arrive in an update.

Reset the account

If Outlook is connected but not updating, the cached data may be damaged. Resetting the account makes Outlook download a fresh copy from Microsoft 365.

1. Make sure your Mac is connected to the internet.
2. In Outlook, choose Tools, then Accounts.
3. Select the account that is not syncing.
4. At the bottom, choose Manage, then Reset Account.

This deletes any information that has not synced to the server. That is why you should make sure your Mac is connected first.

Give it time

A reset or a long network outage can leave Outlook with a lot to rebuild. Large folders, especially Deleted Items and Sent Items, can take a long time to catch up. If Outlook looks stuck, it may just need time. Repeating resets or reinstalling can restart the process.

Shared mailboxes and calendars

If your main mailbox works but a shared mailbox or calendar does not, the cause may be permissions or how it was added. If the web version looks right and the Mac does not, resetting the account usually helps.

When search looks like a sync problem

If the emails are present but search cannot find them, the search information may need to be rebuilt; that is different from a sync problem.

Remove and re-add the account

If none of that works, remove the account and add it again to rebuild it cleanly. Try the simpler fixes first. For a business account, check first that other people are not affected too.

When to get help

If Outlook on the web is also missing mail or calendar data, the problem is with your Microsoft 365 account, not your Mac. If the problem affects shared mailboxes or several people, or keeps coming back, it is usually better to look at the whole setup. See our Microsoft 365 setup guide. If Outlook opens but will not let you edit or save, see our guide to Office 2024, Office 2019 and Microsoft 365 on a Mac.

Need a hand?

If you would like help getting Outlook syncing again on your Mac, contact Your Mac Tech.