MX pointing to an IP address

[Barry Margolin]

In article <93sls5$k0a at pub3.rc.vix.com>, Jim Reid  <jim at rfc1035.com> wrote:
>>>>>> "Frank" == Frank Krychek <jojo at intnet.mu> writes:
>
>    Frank> Is it legal to have an MX record that points to an IP
>    Frank> address instead of to a hostname i.e
>
>    Frank> hostb IN MX 204.5.6.7
>
>No. Read RFC1035 on the syntax of MX records. You've missed the
>preference value in the record's rdata. And the final element of the
>rdata is a hostname, not a dotted decimal IP addrres. That hostname
>must exist as an A record.
>
>    Frank> What potential problems could this lead to?
>
>Undeliverable mail. DNS errors at load time, leading to lame servers
>and failing zone transfers.

Using an IP address instead of a hostname will *not* result in an error
from the DNS server at load time.  Syntactically, an MX record pointing to
an address is valid (assuming he puts in the preference level that he
accidentally left out above), so named won't complain.  But most mailers
will.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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