70:  Why can't Emacs talk to certain hosts (or certain hostnames)?
  
  The problem may be that Emacs is linked with a wimpier version of
  gethostbyname than the rest of the programs on the machine.  This is often
  manifested as a message on startup of `X server not responding.  Check     +
  your DISPLAY environment variable.' or a message of `Unknown host' from    +
  open-network-stream.                                                       +
  
  On a Sun, this may be because Emacs had to be linked with the static C
  library.  The version of gethostbyname in the static C library may only
  look in /etc/hosts and the NIS (YP) maps, while the version in the dynamic
  C library may be smart enough to check DNS in addition to or instead of
  NIS.  On a Motorola Delta running System V R3.6, the version of            !
  gethosbyname in the standard library works, but the one that works with    !
  NIS doesn't (the one you get with -linet).  Other operating systems have   !
  similar problems.                                                          +
  
  Try these options:
  
  * Explicitly add the host you want to communicate with to /etc/hosts.
  
  * Relink Emacs with this line in src/config.h:
  
      #define LIBS_SYSTEM -lresolv
  
  * Replace gethostbyname and friends in libc.a with more useful versions
    such as the ones in libresolv.a.  Then relink Emacs.
  
  * If you are actually running NIS, make sure that `ypbind' is properly
    told to do DNS lookups with the correct command line switch.
  
  * Use tcp.el and tcp.c from GNUS.  This has the additional advantage that
    you can use numeric IP addresses instead of names.  open-network-stream
    currently can't handle numeric addresses.  Brian Thomson
    <thomson@hub.toronto.edu> has a enhancement to open-network-stream to
    allow it to handle numeric addresses.