I created a simple document - just text - in LO, saved it as “whatever.doc”. It opens in LO. I emailed it to a friend. He says Word won’t open it.
Did you save it with extension doc, or did you really save as Word file?
If all that you want is e-mailing a document, simply choose File → Send → E-mail as Microsoft Word from the menu. Thus, you will be on the safe side, as this feature converts a document to a DOC file, not to a DOCX that is much more problematic.