I liked at ->mime_type which is "application/octet-stream", but I am not aware of other information options.
The attachment in the actual email is fine as far as I can tell. I have about 46 emails, each with a single attachment, which is about 10 Mb, which composes a 460 Mb 7z file as a whole.
How do I check the raw data? I thought that was what I was trying to output, which comes out as zero-length, although, spot-checking would suggest it might be being overwritten for some reason, as I do see a non-zero length during then zero-length at the end.