Files from slack sent in an email does not open

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Attachments on the email sent using front can not be opened.
The scenario is getting the files from a Slack msg and attaching them to a front email. but the recipient can not open the files.

Excel cannot open the file ‘file.xlsx’ because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.

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