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Mailman HTML editing error
If you are receiving an error "The page you saved contains suspicious HTML that could potentially expose your users to cross-site scripting attacks. This change has therefore been rejected. If you still want to make these changes, you must have shell access to your Mailman server. See FAQ 4.48. Page Unchanged." the problem is caused by having <link rel="SHORTCUT ICON" href="<mm-favicon>"> or a similar link to a style sheet.
The solution is to embed the styles in the page and give up on your favicon.