Relevant Products: Signature Manager Outlook Edition
You are using Exclaimer Signature Manager Outlook Edition, and you notice that hosted images are blocked in digitally signed emails.
As of 09/10/2018, by default, the external content is blocked in Outlook when emails are digitally signed. For more information, please see the following Microsoft article.
If your signature templates are using hosted images, they will need to be updated to use embedded images.