Brian,

I've gotten similar reports in the past couple weeks but since it was always Outlook or Mac Mail users using IMAPS I never gave it much thought and assumed it was client-side corruption and just wrote it off as that. (To err on the side of caution we did reindex their folders and even ran a repair on their accounts just to eliminate server-side but customers reported problem persisted even after they removed the account and re-added it to their email client). Now that I've seen this I am going to have to back and see if I can reproduce this on those accounts as well.

Post-Script: Seems to have started with Build 8923 for us.

We have the same on some of the mobile clients. We cant pin it down and have opened a ticket which is now closed.

NOthing gives it away afaik.

We've been struggling intermittently with this as well.  Clients will report Outlook and Mobile device display different emails from each other, which in turn are different from Webmail.  In our experience, EAS (mobile) tends to have a LOT fewer sync issues than MAPI (Outlook).  In fact EAS has so few noticeable problems that we consider it "reliable".  

MAPI on the other hand-- we can't get through a single week without calls about MAPI trouble.  We usually assume it's cache corruption in Outlook, and usually-- but not always-- Outlook and Webmail fall into sync when the user deletes the Outlook profile entirely, cleans up the old account files locally, then creates a brand new profile with a different name and adds the account to it.  Once it sucks down the original message set from the server, it's back in sync.... unless it runs into corrupt messages, which tends to cause sync to fail again.

We've tried using the manual Sync option found under the Connectivity page and sometimes that works, but it's hit-or-miss enough that most of the time we go straight to the new-profile route-- saving the resync button (on a click-and-pray-it-works basis) mainly for those users who don't know how to do the profile cleanout, or refuse to spend the time and demand WE fix the problem.  It also preserves the auto-fill cache.  Deleting the profile also deletes auto-fill cache, and you'd be surprised how many users have an absolute stroke over that.

 

@Jay Dubb... The auto fill cache!!!🤦‍♂️🤦‍♂️🤦‍♂️ if it wasn't for that, recreating the profile would be simple. That's why I always hesitate to delete profile.

So we are seeing the same things and only seems to be one customer that is using Outlook 2016 on windows 10. We have completely deleted outlook profiles and OST files and pretty much everything else poster have stated here. We had a ticket open with SM but was not able to find much as it is random. We have moved one of the users over to EM Client and seems to have gone away but the user can't say for sure after 30 days as it is random.  

To add to the list of issue user reported opening an email, start to read and then completely just close/disappear and then they could not find it any longer. Happens on drafting emails as well. Some of them we would find in the sync error folders in error/conflicts some not at all.  Checked AV to make sure that was not an issue.

This was at least reported to start about 60 days and we are fare behind at 8888 as this is only customer it is happening to but we will be going current this weekend and test some more. We where able to find one of the user where we are currently getting sync error in the delete items all the time even with the folder on the server completely empty.

One of the thoughts is a Windows and or Outlook update that is messing with this.

How to backup the autocomplete list in Outlook

https://www.lifewire.com/back-up-copy-auto-complete-list-outlook-1173775 

@Rick Baranowski wrote:  To add to the list of issue user reported opening an email, start to read and then completely just close/disappear and then they could not find it any longer.

We have been seeing that as well.  Our admin has opened several tickets about emails that just disappear without a trace, but so far each ticket ended up being closed without SM being able to duplicate or substantiate the complaint.  

We just had another couple mysteriously disappear on Friday, but the customer didn't want to press on with diagnosis, because the missing emails were forwarded to a manager (originals went completely missing in the mailbox of the person who forwarded them, after forwarding) and they just went to the manager's mailbox to get a copy of it.

When we open tickets, it often requires our admin to connect with the customer's on-site IT staff, who in turn have to interact with the user with the problem.  And sometimes the customer's IT team doesn't have time to go through another round of connect-the-dots with us to satisfy ticket requests, thus some of the instances go unreported.  But to be fair, we've opened our fair share of tickets on it.