What is Mail Attachment.as ? And how can get rid of it?

I have an email address which is associated with my Godaddy webmail account that is run by Microsoft 365. When I send an email through Apple Mail and add a .docx or .doc attachment to the email, it turns into a file entitled Mail Attachment.as which I can't open nor can the people to whom I send the attachment. It only seems to do this when I am sending an attachment through Apple Mail using that particular address. If I send it directly from the Godadday Webmail, it doesn't do this.

Can anyone help me get rid of this?