When editing a new mail or reading one, the images to send, save as draft and so on doesn't specify any alt attribute.
I know that a popup is shown, but it could be ignored by some browser.
In fact a non-decorative image must have its own alt text accordingly with w3c guidelines.
I am posting it as a bug because it could frustrate blind users, or users who use a textual browser such as elinks (i do that sometimes).
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LtWorf