If you mean include an arbitrary binary attachment (say an executable file) displayed inline in the archived message rather that removed and replaced by a link, then no, there is no way to do that.
If you mean replace the attachment with a link that preserves the original attachment file name and extension, put the following in mm_cfg.py
SCRUBBER_DONT_USE_ATTACHMENT_FILENAME = False SCRUBBER_USE_ATTACHMENT_FILENAME_EXTENSION = True
That is precisely what I was looking for, thank you very much.
The root cause of the problem was - People are starting to use docx and xlsx files by default now, and these mime types aren't recognized (at least in the version of mailman that I have.) So they get renamed "attachment.bin" and that's a problem for non-technical users.