Offtopic!
Here is, thanks to MJR for hint on MIME, how you reply in thread while receiving the digest, using kmail.
First you set as he suggested the digest form to be MIME.
When the digest arrives, open it, then click on the Encapsulated message heading for any particular post, such as this one.
Then click and hold down Reply. It gives the option of reply to the list, which when you take it, results in this message.
Hope this really does come in thread. It is a bit odd that it does not find the address itself however, you have to supply it manjally, so maybe it won't....
Peter