Microsoft Office 365 and Office.com paid accounts may block Jeeng ad units and prevent them from showing up in an email. Even with a CNAME and HTTPS setup, these email clients will block our ads if the domain has enabled their Safe Links feature. This would typically happen for ads that are new and have not been verified by their system.
There is no workaround at this time other than to disable the Safe Links feature.
What you might experience is one of our "default" (non-paid) ads. This will generally appear as a Wikipedia article, which we present so there aren't broken images.