> It used to be that large, lenghthy messages were discouraged
> in listserv list mailings--problems for the network, some
> mail systems having troubles handling such messages, etc.
> Is that still the case? Would messages of 400 or 500
> lines cause serious problems?

It's between you and your subscribers.  Personally I don't
hesitate to post messages of that size to lists that I
control.  LISTSERV can handle it easily.