PTR records

[Everton da Silva Marques]

Joseph wrote:
> Again, there are certain times when you MAY NOT use CNAME records.
> When there is another record for the same name (e.g., SOA, NS, MX).
> When it is an NS or MX record target.
>
> Why have CNAMEs?  Single-stop changes.  Instead of having to stop at
> each use of the name and decide whether it should be changed.  I could
> have two sets of names:
>
>	franklin	IN A		...
>	mail		IN CNAME	franklin
>	pop3		IN CNAME	franklin
>	mailhost	IN CNAME	franklin

I´m assuming the above zone also has an MX RR like the following:

			IN MX 	10 mail

But the first paragraph seems to state the MX records can´t point to
an CNAME RR. Am I missing anything?