How can I tell a host name from a subdomain

[Barry Margolin]

In article <bgrr15$2njp$1 at sf1.isc.org>, Sam Kong <ssk at chol.net> wrote:
>Then do you think that a host name is also a subdomain?
>Subdomain can have many hosts in its domain.
>But host is just a computer and can't have lower level nodes.

That's not true.  yahoo.com is a hostname, but that doesn't prohibit
www.yahoo.com.

>And also
>user at subdomain.domain.com is possible but
>user at hostname.domain.com is not.
>
>Or am I wrong? I am not sure.

You're wrong.  user at hostname.domain.com and user at subdomain.domain.com are
processed exactly the same way:

1. First look for MX records associated with the name after the @; if any
   are found, try to send the mail to those servers in order of the
   preference levels.

2. Otherwise, look up the A records for the name, and try to send the mail to
   those addresses.

The existence of other names that have the name as a suffix are irrelevant.

-- 
Barry Margolin, barry.margolin at level3.com
Level(3), Woburn, MA
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