Might be related to MIME.  Have them try

SET listname NOMIME

At 13:15 07/28/1999 Wednesday , erin mckeon wrote:
 >people have been telling me that when they receive their digests, it
 >comes without individual headers (in other words, there's a header for
 >the digest itself, but each post within the digest has no indication of
 >who/where it came from)