That’s a bit vague. There is metadata that is part of the file (like the Producer of a PDF) – that will, of course, be preserved. And there is metadata, like Finder comments, creation date, keywords, that exists separately from the file proper and lives only in the file system, not the file itself. Those will not be transmitted with the file attachment and consequently can’t be saved.
You don’t. The creation date is not part of the file, it’s a property of the file system. You get sent a file, not its creation date. That’s a feature/short coming of MIME etc. Your best bet is to receive PDFs which contain the creation date in their metadata, i.e. inside the file. You can then extract it with a script and use it to set DT’s creation date.