Using a group policy object to disable signatures in Microsoft Outlook
Issue
You have installed Signature 365 and wish to prevent users on your domain from creating their own internal Outlook signatures or wish to disable the internal signature functionality of Outlook completely.
You may also wish to remove any existing signatures that your users have created or have been deployed by another solution within the internal Outlook signatures feature.
Solution
You can use the Symprex Email Signature Utility to perform both of these functions - please see the following Link for information on how to achieve this.
Outlook (Classic) agent release notes
See release history, fixes, and updates for the Signature 365 Outlook Classic agent.
Using Sent Items Update does not work when sending on behalf of another user
Why Sent Items Update cannot update messages sent on behalf of another user, and the current product limitation.