MX pointing to an IP address

[Jim Reid]

>>>>> "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.