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why does a black vertical box appear on my email messages in outlook online? It blocks text. It has a "close" button on it that is not active. Please help!

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some messages that I receive via outlook have a vertical black box on the right side of the screen that blocks text. It is only true in firefox. it may be related to screenshots in the mail itself or to attachments.

some messages that I receive via outlook have a vertical black box on the right side of the screen that blocks text. It is only true in firefox. it may be related to screenshots in the mail itself or to attachments.

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Could it be a vertical advertisement that you are partially blocking? Maybe a screenshot would be helpful. You can attach an image to a reply using the "Browse" button below the compose area.