I should add that my "nothing inherently wrong" is strictly only 99% correct. It is not very common to format emails like that. A canonical form of robthebold's "bad" message would be four parts. The first part nested, with a plain text and HTML sub-parts, then the other three parts for the attachments. Grouping the attachments like in that message may be seen as ambiguous. Technically, it has a single attachment containing three files.