KMail already uses this icon in it's menu and context menu. I think this alsoFor other statuses
we already use mail-* icons too. I think this also more correct since according
to the standard the emblem icons are "Icons for tags and properties of files,
tags and properties of files, that are displayed in the file manager".
https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html#context