> But wouldn't it also be possible to build a heirarchy of MX records like
> host.domain.ucar.edu MX 100 bastion.ucar.edu
> MX 1 host.domain.ucar.edu
> and avoid the split DNS altogether? Hosts that can't get to
> "host.domain.ucar.edu" would send mail to "bastion.ucar.edu"
> bastion would send the mail to "host.domain.ucar.edu".
Two problems with this. First of all, I don't control the DNS for every
subdomain. I would have to rely on every group sysadmin to install the
proper MX. Granted, if they didn't then their users couldn't get mail,
but this isn't very appetizing. Second, even if I did this, it would
require every outside machine that wants to send mail to one of our
hosts to first fail to initiate a direct connection to the host before
sending to the bastion. This is at best rather unfriendly to the sites
trying to send us mail. I'd rather not do that. Again, the split DNS