[hacknews] mail fixes

henry (04/29/83)

Fixed a serious bug in mail(1) that caused it to try to create an
infinite-length file in some cases (an internal buffer overflowed
on a very long system name).  Also did some general cleanup and
improvement of error messages.  The infinite-file bug more or less
caused this afternoon's "crash" (which was actually a deliberate
shutdown when /tmp ran out of space!).