Usermin webmail links blocked in iframe (CORS & "bad" senders)

SYSTEM INFORMATION
OS type and version Ubuntu 22.04
Webmin version 2.641
Usermin version 2.540

Think I’ve found something that constitutes a bug.
A usermin user trying to click a link in an HTML email was “blocked” due to CORS, because the HTML email was (mal-)formatted using target="_self" attribute which result in links trying to open -inside- the iframe.

I had them try the option to open links in a new tab, toggled it between its two available options, but this didn’t change anything about how links worked. (Maybe I misunderstand the option, maybe its bugged, or not documented clearly enough to avoid assumptions on my part.)

In any case, I don’t think the webmail client should ever allow opening a third-party website inside the clients email-viewing iframe. I think the emails should be sanitized for display in the webmail, to strip out or replace the target="_self" attributes and other problematic target values.
Couple ways to do it, server-side HTML Parser or leverage clients own javascript to make sure things are updated as they should be.