Mac Mail not Syncing with Exchange email server on MacOS devices

I agree its is a reoccurring issue with the Mail app and Exchange. I had it several times in the past too but have the feeling it is triggered by large mailboxes. So what i did was:

• clean up my mail box and archive older mails locally to bring my inbox <10GB
• delete the exchange account
• delete the Exchange folders from Library/Mail (in my case the folder was V8)
• empty trash
• reboot
• reinstate the Exchange account
• wait till it has fully synced

I noticed that rebuilding and syncing takes a lot of time (indeed up to 3 days depending on the size of your inbox) during which the Mail app has its own way of syncing and not necessarily prioritizing the Inbox over subfolders. To overcome this in order to retrieve the latest mail during this period, i noticed it helps to restart mail after which the latest mail in the inbox will come in. You may need to repeat this until all mail has been synced.

Hope this helps and someone at apple also starts reading this

Thank you for all of your posts! I was struggling to get my Exchange mail account to work on my new MacBook Air running Big Sur 11.2. Nothing worked (deleting account and recreating; turning off all Apple devices; a call to tech support; sending myself an email from Mail). Finally, I opened outlook in Safari and deleted the thousands of files I had in bulk mail, junk, sent, drafts folders. I also deleted some mail folders to clean everything up. I synced my mail, rebuilt the mailbox, and restarted Mail several times. Finally, it worked! I believe the issue was with having too many emails in Exchange to sync.

Had the same issue. Solution was to delete and set up Exchange account again. It looks like authentication process has change hence needed 'refreshing'. It is now working normally on Apple Mail.

I think I finally fixed this on my Big Sur M1 Mac Mini by deleting the MailData folders, but probably more importantly, using OWA and Outlook to move messages out of my Sent folder and one of my main folders that I use for filing messages. Both were over 10,000 messages so I started filing messages in other folders by year so my main Sent folder and archive folders are smaller. There shouldn't be a hard limit on the number of messages in a folder, but this has helped me in the past and appears to have fixed this once again. It's incredibly annoying.

For the avoidance of doubt - there are two problems; both of which I had.

Problem 1: suddenly mails read on MacOS Mail are no longer seen as read elsewhere; the exchange server is not updated. This only happens with an exchange server. The solution for me is to delete the whole account and reintroduce it and it works again. For a bit.

Problem 2: suddenly emails no longer arrive on MacOS Mail. This again only happens with an exchange server. The solution for this is (bizarrely!) to completely switch off your phone and/or other iOS devices. Mails arrived within minutes of me doing this.

There appears to be a cross-over: since I switched off my phone and deleted by exchange account on my MAC whilst the phone was off, then reinstating it Problem 1 has gone away completely - I had to delete my exchange account every few days up to that point.

It is broken, that's for sure.

update: I deleted the Exchange account (after saving all emails) and then reinstalled it and seems to have fixed the issue

UPDATE: I turned off my phone and restarted my computer and all is magically working perfectly again. Go figure. My guess is some of these replies where it starts working again spontaneously, the user turned off their phone sometime in the course of the problem but didn't make the connection to the resolution of the issue on the computer. Anyway, I'm sure there are many sync problems this doesn't solve - but it solved mine! Thank god for this forum, otherwise I would have been trying to delete libraries and rebuild caches or all kinds of other things I probably would have screwed up. :)

I've been experiencing this problem as well and tried rebooting but still had issues. I then tried sending an email FROM the account that wasn't syncing and then all of my new mail came in.

I had a similar problem when my company moved to an exchange server. After a few days, I found out that I would read email on my mac (and move some to specific folders), but on my iPhone and iPad, those mails would still appear as unread, (and for the ones I moved, they would still be in the inbox).

I then looked at the mail using the outlook web app. What seemed to happen is that anything being done on mac mail was not reflected on the exchange mails: I would for example flag a mail on mac mail: the mail on exchange would remain un-flagged (which is why the other devices did not see the change either). But it worked fine the other way around: flagging a mail on exchange (via the outlook web app) was instantly reflected on mac mail.

To cut a long story short, the only solution that worked was to fully delete the exchange account from the mac, and recreate it.

Note that I never had an issue with receiving or sending emails: that always worked. It was just that reading mail on mac mail was not being reflected in exchange. Let's see for how long that solution lasts ...

Have the same problem. None of the suggestions work permanently. Deleting Mail's saved application state worked for a while a couple of times on Mojave. Not on Big Sur. Using Office 365, and Outlook for Mac (which I despise) works fine. Web Outlook (which I despise even more) works fine. Mail app on iPhone works fine. iCloud account mail works fine. The only thing that is unreliable is an exchange account in Mail on Mac OS. This is not a new problem. For me, it has been going on for years, dating back to when I had my own Exchange server. Office 365 is no better. I have over 350k messages in archives mostly on my mac and some in the cloud on office 365. Deleting and reinstalling my Exchange account takes about 3 days to synch and only temporarily solves the problem. It is incredibly frustrating. You can search the forums here and find issues dating back to Catalina. Work arounds are inconsistent such that they seem to work only by coincidence. Somebody once told me that Apple pays Microsoft licensing fees for using Exchange on iOS, but does not pay the fees on Mac OS. If that truly is what is going on, it is ridiculously hypocritical, petty, and insulting. If it is not the cause, then something else out of user control has to be the problem. I really, really wish Apple would resolve this. Maybe Apple could have the developers for the iOS Mail app give a seminar or two to the Mac OS Mail developers.

There is another factor that you may or may not be factoring in -- the synch process does not just depend on the devices, it also depends on the Exchange server. The Exchange server may be getting behind the scenes updated software, patches, etc. that you might not be aware of. That can disrupt the process. Sometimes software updates are performed on the Exchange server and it takes multiple steps or tries by the server people to resolve new issues that are introduced. It's hard to see how downloading mail on an iPhone would stop the Mac from downloading unless there is an issue on the server side, which might have been resolved during the time that you and others were noticing these changes. We use MS-Exchange at work and I am on the distribution for the IT Group and what is happening on the server side. There are issues from time to time, they are constantly making server updates and security updates. I specifically recall instances where the iPhones were able to download email but the Macs and/or PCs were not updating, sometimes lasting for many hours.

Like SiliconeCatastrophe, I do not have any iOS devices, but my MBP (Retina, Early 2015, running macOS 10.14.6) is showing this behaviour too.

A couple of weeks ago, Mail from my work Exchange server stopped syncing to the Inbox, although I could still send from the account. I would get an occasional burst where it updated, but unpredictably and roughly once a day. Forcing a rebuild of the mailbox got the mail to appear. Deleting the account and replacing it did not seem to cure it - obviously that triggers a mailbox build, so new mail appeared but was not syncing after that.

I started trying other clients (Spark too intrusive, Thunderbird worked fine but not a fan of the interface) and then Mail started working again. Until yesterday, when it stopped syncing again.