DavidR
5
If this is a regular email and the newsletter has the same remote source (where it looks for the iFrame content), and you are happy it is OK then you can add this remote address (URL) to the Permitted URLs list. Internet Mail, Customize, Heuristics tag, Permitted URLs and Add the URL, see image.
It is more a case of investigating like you are doing and if a legit use and source you can add the remote address.
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