Synchronization is unsuccessful after mailbox items are changed through EWS calls

Sometimes when running Outlook in cached mode, users experience  "synchronization is unsuccessful after mailbox items are changed through EWS calls" issue.

Here at Ibmi Media, as part of our Server Management Services, we regularly help our Customers to fix Outlook related errors.

In this context, we will look into the causes of this error and how to get rid of it.

What triggers "synchronization is unsuccessful after mailbox items are changed through EWS calls" issue?

Basically, when you run Microsoft Outlook 2013, Outlook 2016, Outlook 2019, or Outlook for Office 365 client in cached mode, and close your Outlook client and then reopen it later, changes that were made to the mailbox items while Outlook was closed are not synchronized as expected.

These changes triggers issues when mailbox items are changed by using Exchange Web Services (EWS) calls. These changes are sometimes performed by archiving solutions.

Therefore, in these cases, the synchronization failure is expected for Outlook in cached mode.

How to fix the issue when the "synchronization is unsuccessful after mailbox items are changed through EWS calls" ?

To fix this issue , we can use different approaches.

1. Cached Outlook clients

Basically, clearing offline items from the folder where the sync failures occur can help to fix this issue for cached Outlook clients. To do this, follow the steps below;

i. Start by clicking on the specified folder that we wish to clear all offline items from.

ii. Next, do a right click on the folder and then select the Properties from the right-clicking menu.

iii. Now, select the General tab from the Properties dialog box.

iv. Then click on the "Clear Offline Items" button.

v. You will see a warning dialog box prompting you that "Your data was removed from your Outlook data file (.ost)". Now click on the OK button to proceed to next page.

vi. Finally, click on the OK button in the Properties dialog box.

2. By Using Outlook in online mode

To do this, follow the following steps;

i. Start by clicking on the "File" menu >> "Account Settings" >> "Account Settings" again.

ii. Next, select the name of the Microsoft Exchange Server account from under the Email tab.

iii. Now, click on the "Change" button and then "More Settings".

iv. Then, click on the "Manually Control Connection State". Here, select "Connect With the Network". This setting will cause Outlook to start in online mode.

v. To close the settings dialog box, we click on the "OK" button. After that, we click "Next" and "Finish" to exit the Change Account window.

vi. Finally,  click on "Close" to exit the Account Settings window.

Note that Outlook depends on several MAPI properties to govern cached mode synchronization. The specific properties that Outlook uses are PR_CHANGE_KEY and PR_PREDECESSOR_CHANGE_LIST.

In this scenario, the values for these two properties are decremented instead of incrementing when messages are altered through EWS calls, and that action leads to the sync failure.

Need to fix "stuck with synchronization failure" in Outlook? We are available to help you today.


This article will help to solve "stuck with synchronization failure" in Outlook which happens when running Outlook in cached mode.