default mail address host solution discovered

[Barry Margolin <barmar@think.com>]

Well, we finally got our Zmail sources today, and one of the first
things I discovered is that there is an easy solution to the problem of
getting an appropriate default host for addresses typed with no explicit
host (I think we asked Symbolics about this earlier this year and they
didn't know the answer).  The normal default is to use the host from the
user's MAIL-HOST namespace field, but this is often not what is wanted
(in our case, many users receive their mail on our Lispm file server,
but we want all local addresses to specify our Unix mail server, so that
it can do duplicate elimination during mailing list expansion).  It
turns out that there is a special variable
ZWEI:*DEFAULT-HOST-WHEN-PARSING*, which can be set to a host object or a
string; in the latter case it is expected to be a domain name.

The only problem this leaves is getting the right host in the From:
field.  I suspect this can be done with appropriate template hacking.

                                                barmar