Using Sent Items Update does not work when sending on behalf of another user

Scenario

You have send-as permissions on another mailbox and wish to use the Sent Items Update function to update the sent item when sending from that mailbox.

When you view the sent item, you notice that the signature is not present on the email

Reason

When an email is sent from a shared mailbox, the message is saved in the sent items of the sender, not in the sent items of the shared mailbox.

Information on the sender is not included with the sent message, and the Signature 365 Sent Items Update feature cannot identify who sent the message, meaning the item cannot be updated.

Solution

It is possible to configure the Outlook client to place the sent item in the mailbox of the mailbox the email is sent as, rather than the sending users sent items.

You can set the DelegateSentItemsStyle registry value on the Outlook client to achieve this.