Mac Mail (10.15.6) not syncing with Exchange

For those of you (like me) who were still having this issue on Big Sur (email slow to arrive or not arriving at all in Apple Mail for Microsoft Exchange 365 account), this may help, particularly if you have a large number of emails on the Exchange server.

After deleting and reinstalling the exchange account, as advised in this thread, the problem got worse for me. I had to log out of my account on my laptop (16” MB Pro) or restart it to get any exchange emails at all, and then up to about 10 new emails would come in at once and then no more until I logged out/restarted again. Quitting the mail app and reopening it didn’t help, only complete log out/restart. Note that my iPhone and iPad were getting the new emails without any issues

I opened the Apple Mail “Activity” box that can be used to show what the mail app is doing (drop down menu in toolbar under “Window”). This revealed that there were still over 36,000 emails to download. Obviously a hang-up from uninstalling and reinstalling the email account. Clearly it was taking a very very long time to synchronise. Note this was 3 days after I had reinstalled the Exchange account and almost the entire time my laptop had been switched on and connected to internet. I noticed that virtually any mail related activity seemed to really slow the sync process.

I was able to leave my laptop switched on and active over the weekend on a fast internet connection, and I disabled the sleep process so it could download the emails more quickly. Once the number of emails to download fell below about 30,000 the new emails started coming in, although still a bit delayed. As the number continued to drop the emails came in quicker and quicker until there was no delay below about 8,000 remaining.

The mail app has now completed the synchronising process and I am receiving all emails without any delay. Therefore I assume that reinstalling the account worked as hoped in solving my original problem, it just took a few days to sync everything back up.

It appears that the Syncing problem has been resolved in Catalina 10.15.7 as well.

Now exchange mails are coming in at similar time in Mail and in Outlook (running on the same Mac).

BUT, Mail has became a huge Energy and CPU consumer. Watch the Activity Monitor and you'll see it on top.

While Outlook is down the list.. It appears that Mail is performing extra work for some reason (note to Apple...)

after removing the account verify that the folder for this account under ~/Library/Mail/V8 is also deleted

deleted if it's still there.

make sure that your Inbox is not to large (I say no more than 1000 messages) and the rest are in folders (not under the inbox)

After arranging my Inbox (using outlook and not mail) to be smaller everything is working and hope it stay this way

Has anyone considered that the issue might not be mailbox size related? But a large number of emails or volume of data simply increases the chance that something in there is messing up the database? Hence the issues with the inbox. It might even affect IOS as well, but as IOS devices store smaller volumes, the chance of being affected is smaller. And any IOS issue would probably land in a different forum.

I'm mentioning this as my mac mail has been running flawlessly for a month or so after deleting some large emails in my inbox, and emptying my drafts and trash folders. I'm certain that by now my inbox is larger than when the issues first occurred. What if just a single email not stored correctly can cause temporary syncing problems, and multiple faulty emails block syncing altogether? MS Outlook isn't affected, as it has an a differently structured DB.

Never did any mailbox rebuild, or log off/on, or reinstall my exchange account. All running fine. *knocks on wood*

I might have stumbled on a solution after having this problem. On my work computer where I do most of my emails Mail did not sync if I was sending or reading mail while Outlook worked. But once sent via Outlook, mail appeared in the Mail application. On the extra Mac where I play music it was Ok both before and after Big Sur upgrade. But as I was planning to do a backup via Mailsteward of my Mail accounts, I dragged a bunch of mails to a local folder and noticed that Mail app got stuck in moving mails. So I did a backup of all mail accounts, then deleted all local folders containing mail from exchange accounts plus all drafts of mail stored on server. And now my Mail app syncs with exchange server on all my devices (2 Macs, iPad and iPhone)

Many of us have had mail Sync issues these last 6-8 weeks. With some, over time, it corrected itself. Mine took 6 weeks plus. All of us tried rebuilding mailboxes , archiving old mails etc. Most solution created a one time Sync fix, some a multi Sync but none a full fix. I switched to both Spark and outlook and both worked fine as a bridge solution. If you're married to mail (I was) I kept my MAC at latest version software (BIG SUR) and then one day it started working again and never stopped (3+ weeks now) and 2 BIG SUR updates. It's a MAC/MS issues that they appear to be fixing in the backend (account by account it seems). My advice would be to use another email app (Spark or Outlook) and wait for mail to start functioning again. Don't waste time trying fixes as I did.

Good luck.

The only solution right now that seems to work reliably is to connect to Exchange as an IMAP client, rather than as an "Exchange" client.

I'm currently running two parallel connections to the same account, one IMAP and once "Exchange." This makes it trivial to see when the "Exchange" client works correctly and when it falls behind. And the answer is ... there's no obvious pattern. The IMAP client does work reliably, all the time, as far as I can tell. However, it can be somewhat slower to react than the Exchange client, when the latter is working.

The primary downside of using IMAP is that calendar invitations don't work correctly. There's a setting in Exchange that asks that they be included as .ics files, or something like that, which I turned on - but I still don't get directly usable invitations. Fortunately, the invitations do come through on the "Exchange" side and go directly into Calendar. So ... I'm continuing to keep both connections live, which of course means there are two copies of every email (and getting the IMAP connection working the first time took several days as the data was downloaded).

Someone gave the instructions way back on this very long chain. Here's the summary that I kept and used:

Set up a new mail account but don't do it as via Microsoft Exchange. Instead, do the following:

Mail, Accounts, '+', 'Add other account', 'mail account' [This varies a bit by MacOS version. Somewhere as you add an account, you're asked to specify what kind of account it is. A bunch specific possibilities are offered, like iCloud and Exchange and Google (gMail). You don't want any of these - you want "Other", which is a generic IMAP or POP account]

Enter your username and password

On next window, ignore where it may say Unable to verify username or password

Incoming and outgoing mail server should say outlook.office365.com

This is specifically for accounts that are served from Office365. If you're using some other Exchange server, you'll have to provide its address instead.

I believe it's possible to disable IMAP access to an Exchange server. If the server you need to connect to has it disabled, you'll need to convince your mail admin to re-enable it.

-- Jerry

Hi,

I've had this issue for the two last months on Catalina and Big Sur.

The theory of some emails stuck in limbo thus blocking the refreshing process seems to be it.

I've found that a succession of switching to all of my exchange's folders from the left Menu on main screen (where all folders of all accounts and favorites are listed) triggers a refresh of the said folders.

Once they all have been given a chance to refresh, the emails start to arrive again from the Exchange server.

Please give it a try and comment if it works for you.

Hard to believe, a minute after I wrote the email above I deleted the Exchange account an set up a new one for the 11th time and bingo it worked.

So, you have to post about it, then create a new account and it magically work?$(%&#)#

I am running the Big Sur (11.1) OS on my MBP and recently encountered a version of this problem: Mac Mail failed to sync reliably with my work Exchange account. In order to force a sync I would have to quit and restart the Mac Mail app, and sometimes even to reboot or at least to log out and log in again. Frustrating.

After reviewing this thread (thanks to all who are contributing) I seem to have resolved the problem.

First an observation: This problem emerged for me after I had recently had a unusually high number of incoming emails in a single day. I don't know if this was a coincidence or not, but I suspect that it may have pushed the total number of messages in my inbox over some threshold limit.

A first failed attempt: Operating with the hypothesis (drawn from this thread) that the problem might related to volume of emails, I first tried archiving thousands of emails from my Inbox by using the Mac Mail application. This did not solve the problem, perhaps because the continuing sync failure left those messages in the inbox on the Exchange server.

As to my remedy: Looking for an alternative, I used the Microsoft Outlook for Mac app (not the web-based Outlook interface) to access my Outlook inbox. I scrolled to the very bottom (i.e., oldest) messages in my inbox and deleted several hundred. Interestingly, these were messages that I had moved out of my Mac Mail inbox some months ago, but they had not been auto-deleted from the host server inbox.

I then rebooted, and the problem seems to have been resolved. I am now back to reliable, "real-time" syncing. Whew.

I am not sure whether my actions actually fixed the problem, or if this was just a happy coincidence. (A number of contributors to this thread have noted that the problem is intermittent.) But I offer my experience as a data point in the larger collective effort to understand this problem.

Hi,

reduce your inbox size, I left a month in the inbox (1000mails) , the rest in folders by years

let it sync all (it takes hours depends on your mailbox size, mine is 30K mail)

better to arrange it with outlook/OWA than create the account again in OS X

for me it works for now but lets see in the next days

Had exactly the same issue.

Had to go into Settings > Internet Account > Remove my Exchange Account and Re-add it

When I re-added it, I got an error saying that I had to log out and re-build the mailbox, which I did.

After the rebuild (which takes hours)- it appears to be syncing again.

Thanks,

I've been facing this issue for about two weeks. Based on closely watching the behavior on my system, and comparing to comments here, here's my summary:

• The observed problem is that Mail.app incoming email from at least Office365 is not picked up. It's unclear whether stand-alone Exchange servers display the same problem. Mail on iOS, and Outlook do not display the same problem. It's unclear whether other mail user agents on MacOS see the problem.
• It's unclear how long the incoming email is "stuck." I've seen it stuck for 12 hours or more; others report that it's eventually delivered.
• The problem occurs only with updates to the default inbox. Other inboxes, including other mailboxes with special semantics (like Trash), are updated correctly. I added a server-side rule that copies all incoming mail from the default inbox to another inbox; that inbox is updated correctly. Outgoing mail is unaffected. Structural updates (e.g., adding a new mailbox folder) may or may not be affected.
• It's been reported that if you directly use an IMAP connection to Exchange - as opposed to the MAPI connection that is created for you by default.
• It was suggested that turning off "Automatically manage server connection settings" would fix the problem. For me, it had no effect at all.
• The problem is unrelated to MacOS version. I'm seeing it on 10.14.6; a scan through this chain of comments shows that it's been observed, in the same form, at least from some version of High Sierra through the latest Big Sur.
• The problem comes and goes. I saw it for the first time, consistently, for several days early in January. Then it disappeared spontaneously for about a week. Then sometime last week - probably around Friday - it reappeared and is still there consistently. [Irony strikes. After several days of not working ... the problem spontaneously disappeared while I was writing this note!]
• For me, restarting Mail.app almost always causes all the held back email to be delivered. (My data on this is a bit "dirty" because usually when I restart Mail.app I also do a "sqlite3 Envelope\ Index vacuum" to clean up my (very large - about 320MB - envelope index. (Almost all of that is from accounts other than my Exchange account.) I'm not absolutely sure whether that changes anything, but I don't think so.
• Because a restart of Mail.app appears to cause the Inbox to be synchronized, and many of the suggested fixes here require restarting Mail.app, the observation that "changing X seems to fix things" has to be considered with great skepticism. X may simply be irrelevant to the problem - the restart itself may be the (kind of) cure. However, if you look back, most of these reports are initially positive - but then the author comes back and says "the problem returned shortly after."

In summary, I think we've learned the following:

1. The issue has something to do with ongoing synchronization of the Inbox using the MAPI protocol. Note that MAPI is a "push" protocol, not a polled protocol. So "Get Mail" on a MAPI connection is a no-op - and, in fact, "Get Mail" doesn't "unstick" the connection.
2. Apparently there's something unique in MAPI about the default Inbox as opposed to every other folder.
3. Apparently the startup handling of (at least) the default Inbox is different from the ongoing update mechanism. This makes sense - typical implementations of "on the fly delta updates" will, on re-connection, compare server and client records to do bulk updates and synchronize the two to get around "state drift."
4. Since this problem has been there through so many versions of Mail.app, and was not triggered by any recent changes in Mail.app, the cause must be a change in Exchange. This does not necessarily mean that it's a bug in Exchange: It could be a perfectly legitimate change on the server side that happens to trigger a long-latent bug on the client side. Given the complexities of MAPI - typical of Microsoft protocols - this kind of thing has happened before.
5. One possible hypothesis is that we're seeing rolling upgrades across the various Office365 servers. Some versions trigger the bug; others don't. It might be enlightening to record which back end servers see the problem and which ones don't.

Because this is almost certainly an incompatibility in the understanding of the MAPI protocol by the two ends, and Outlook and some other clients are not affected, no matter what the underlying cause, Microsoft is not going to be receptive to fixing it. Apple will have to do it - unless Microsoft, for some other reason, decides the change was unwarranted and reverts it.