I would explain to the author that the issue of the file showing 0 bytes (or a significantly smaller size than expected) when attached to an email is usually not due to any deletion or loss of the content by the email provider. Here is what is likely happening:

• Sometimes during the process of attaching a file to an email, the email system or client might not fully process the file correctly, resulting in a file attachment showing as zero bytes or smaller than the actual file size. This can be caused by an incomplete transfer, file corruption during upload, or a problem with the email client's handling of files.
• The file on the author's computer is intact; the issue is with how the email client reads or uploads the file attachment. No content from the book itself has been deleted.
• This situation can occur if the file transfer is interrupted or if the email client experiences a glitch where it assigns an attachment name without including the actual data (the file content).
• The author should try to reattach the file, possibly rename it to a simpler filename, or send the file using a different email client or method (e.g., uploading via a cloud service).
• To reassure the author, the original file on their computer remains safe. The problem is just in the transfer process of the attachment, not in the book file itself.

This explanation can help relieve the author's concern that their book content has been deleted when the attachment shows 0 bytes. The issue is technical and localized to the email system, not a deletion of the actual book content.