Outlook for Mac sync issues

Copper Contributor

I've been having a strange, sporadic issue for the past several months. I'm using macOS Catalina and Outlook 16.35.


Outlook sends and receives new mail just fine. But read/unread state, and moves/deletes don't get synced back to O365. For example I could be working on my MacBook for several hours. During that time I'm sending, receiving, moving, and deleting email with no apparent issues. New mail is coming in and mail that I'm composing is sending, and Outlook isn't notifying me of any sync errors.


But then later I'll check email from another device or from my phone, and all of the mail that I've already cleared out of my inbox on my MacBook is still appearing as unread and sitting in my Inbox on every other device. Restarting Outlook on my MacBook doesn't fix it, but usually if I reboot my MacBook entirely and then restart Outlook on it, Outlook will finally sync everything.


Any idea what could be the issue here? Is there a local cache I can flush?

13 Replies

Hi@Jason Clishe 

This is one of the most outlook common issue, so please try following technical steps:


please let me know if you have further question, i will be gald to help :)


Hello@Jason Clishe 


Please provide me your Feedback regarding my answer :)


Best Regards, 


I have the exact same behaviour, did all the steps you mentioned, but it doesn't get better.

Sometimes a new mail comes in immediately, but usually they're delayed by up to 20 minutes.

When I go to offline mode and back to online, it syncs most of the times, but sometimes I need to do that several times, before it syncs at all.

Connection state usually shows "connected to <mailbox>", sometimes last sync is current, sometimes it's not, but the state clearly isnt synced.


Any other ideas?

Hi @Jason Clishe, I faced a similar issue where outlook would stop syncing indefinitely.  while going through many methods, I just toggled the "New outlook" button and switched back to the old outlook look and it started syncing again. Not sure how helpful this would be, however, let me know in case it works for you as well.

This simple solution worked for me. Thanks.
Same issue here and having to recreate an entire profile with 6 email addresses, signatures etc is simply not a feasible solution for this to happen more than once. Unfortunately the simple workarounds haven't worked for me. Has anyone got any new advice with the latest Outlook for Mac 16.52?

Just had a Chat with support and this was their advice. It's worked for now, will see how it behaves over the next week:


Please remove the account from New Outlook and add the account via Direct Sync method.
1. Navigate to Outlook menu bar at the top of the screen
2. Click on "Tools" -- "Accounts"
3. Click on the "+" sign
4. Type in the email address and click on "Continue"
5. Click on the "Not (Google/Yahoo/iCloud/IMAP)?" on the top right of the next window which appears
6. Toggle the switch next to "Sync with Microsoft Cloud", so it turns to gray from blue
7. After which, select "Google"
8. Type in your password for the email account
9. Click on "Add Account"

@sammond7  I am having the same issue. It is a syncing issue. I manually ran the sync for my calendar and then the information populated correctly.  Because I manage projects and meetings is my thing... my exchange was added to the iCloud mail... that syncs better than outlook. 

works for me too. thanks!



Worked for me too. Reminds me of the New Coke. Bad move.

@Parth_sarvaiya Thank-you. I had the same issue repeatedly, sometimes for hours. Your trick of switching back to the old outlook worked immediately. Thanks!

@Burk57 My version of Outlook no longer has this option to switch back and forth between original and new.  Is there a way to restore that feature?

This worked for me too!