Editing the subject line of existing messages is supported in classic Outlook, but the context does not state that this feature is available in the new Outlook, nor does it provide any roadmap or date for when it will return there.
The available documentation only confirms how to edit subjects in supported Outlook versions and how to resolve cases where the subject cannot be edited due to a collapsed header or specific item properties. It does not announce subject-line editing support for new Outlook or give a timeline for it.
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