I think there is a reasonable solution to be had: Render the content of the iframe at sending time.

That way the client does not depend on accessing anything JQuery, the email has already been composed at origin.

Suggesting re-opening this ticket.

We already support a raw HTML block in the "Drag and drop" email builder.
Jquery would probably never work in an email (limited by the inbox providers).

This is a great idea. It would allow to create automated content that is generated monthly.
For instance, you can have a monthly event and insert the agenda into the outreach email by publishing it as RSS and embedding it on the email body.