Scenario
You are using Classic Outlook and Server-Side deployment. You have enabled the Sent Items Update feature in Exclaimer.
However, you notice that some Sent Items do not show signatures.
Reason
This can be the result of two issues: Cached Exchange Mode, and Exchange Web Services (EWS) access.
In Cached Exchange Mode, Outlook stores sent messages locally and syncs them with the Exchange Online mailbox afterwards. Due to this synchronization delay, Exclaimer may not find the Sent Item when it attempts to apply the server-side signature. As a result, the Sent Items update can fail.
This behavior is caused by how Classic Outlook caches and syncs mailbox data, and it is beyond Exclaimer’s control.
When Cached Exchange Mode is disabled, Sent Items are saved directly to the server mailbox, allowing Exclaimer to update them successfully. If messages still do not appear correctly in Outlook on the web, this could indicate a profile or mailbox issue rather than a signature processing problem.
Exchange Web Services (EWS) access restrictions can cause the request to be authenticated but not authorised.
This is typically consistent with one of the following:
- EWS being disabled at the organisation level
- EWS being disabled at the mailbox level
- EWS access being restricted via policy (for example, Application Access Policy)
Exchange Web Services access may appear to be disabled or unavailable in Microsoft 365 tenants even when no intentional configuration change has been made. In these cases, the Sent Items update functionality may fail as Exclaimer is unable to access the Exchange Web Services required to retrieve and update the sent message. For more information, see Microsoft's resources on this issue.
Resolution
• Cached Exchange Mode sync timing is inherent to Outlook Classic and cannot be controlled by Exclaimer.
• Sent Item updates with server-side signatures are not guaranteed when using Cached Exchange Mode.
• The solution below does not apply to New Outlook.
Select an option below to view the related instructions:
To verify whether Cached Exchange Mode is causing Sent Items to miss server-side signatures, you must set up a new profile, then disable Cached Exchange Mode from the Account Settings of Outlook.
To disable Cached Exchange Mode:
- Open the Control Panel and select Mail (Microsoft Outlook).
- Select Show Profiles, then select Add to add a new profile.
- Enter the new profile name and select OK.
- Follow the on-screen instructions to configure your email account in the new profile. Select Finish when the configuration is complete.
Using a fresh profile ensures there are no existing cache issues or corrupted settings affecting the test.
- Open Classic Outlook using the new profile.
- In the File menu, select Account Settings, then select Account Settings again.
In the Email tab, select your Exchange account from the list.
Select Change…
This opens the Exchange Account Settings window.
Deselect the Use Cached Exchange Mode download email to an Outlook data file checkbox.
Select Next, then Finish.
Restart Outlook to apply the change.
-
Compose a new email. Check the Sent Items folder in the live mailbox (for example, via Outlook on the web) to confirm if the server-side signature appears.
If the signature now appears in the Sent Items, the issue was caused by Cached Exchange Mode and is resolved.
If disabling Cached Exchange Mode does not resolve the issue, verify EWS availability and permissions.
-
Check the organisation-level EWS setting by running the following command in PowerShell:
Get-OrganizationConfig | fl EwsEnabled -
If the result shows that the setting is disabled, enable EWS at the organisation level by running the following command in PowerShell:
Set-OrganizationConfig -EwsEnabled:$true
Depending on your configuration, you may require the following additional checks:
- Verify EWS is not disabled at the mailbox level
- Confirm that no Application Access Policy is restricting Exclaimer service access
- Review Conditional Access policies that may block Exchange Online EWS
If every Sent Item in Classic Outlook must always show the signature, consider using Client-Side signatures instead.
With Client-Side signatures:
The signature is applied before the email is sent.
The Sent Item is saved already, containing the signature.
No post-send update or mailbox replacement is required.
There is no dependency on synchronization timing.
For more information, see the Difference in features between Client-Side and Server-Side signatures.
This avoids the limitations caused by Cached Exchange Mode and ensures that Sent Items displays signatures consistently across all clients.
If the above resolutions do not solve the problem, our Support team can help if you provide some diagnostic information.
To get further help:
-
Run the following command in PowerShell:
Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass; Invoke-WebRequest -Uri "https://raw.githubusercontent.com/exclaimerltd/Internal-Support-Scripts/master/AddInChecks.ps1" -OutFile "$env:TEMP\AddInChecks.ps1"; & "$env:TEMP\AddInChecks.ps1" - Follow the on-screen prompts.
-
When complete, a report named AddInChecks.html will be generated.
NOTE: Report Location:
By default: C:\Users\<YourUser>\Downloads\AddInChecks.html
Fallback (if Downloads is unavailable): C:\Temp\AddInChecks.html - Raise a Support ticket. Add the file generated in Step 3 in the Attachments section of the ticket form. We also recommend reporting your results for the previous solutions.
If your Support request concerns authentication, include an export of the affected user's Entra ID sign-in logs with your Support ticket.
To export the logs:
- Sign in to the Microsoft Entra admin centre.
- Navigate to Monitoring & health > Sign-in logs.
- On the Interactive sign-ins tab, filter by the affected user's UPN and the date range covering the issue, then export as CSV.
- Switch to the Non-interactive sign-ins tab, apply the same filter, and export as CSV.
- Attach both CSV files to your support ticket.