MX lookup problem?

[Kevin Darcy]

Antony Mak wrote:

> Hi all,
>
> Recently, I have found some strange problems with my DNS server. I have
> found that some domains' MX record can not be seen periodically(that make me
> can't send mail to them). I have used nslookup to query these domain. When
> set q=any and query the domain name, the MX record can not be seen at that
> moment. But when set q=MX, the MX can be seen again and everything work
> fine.

Please be aware that ANY does not mean ALL. There is no guarantee that an
ANY query will be answered with every record that happens to be associated with
a given name, scoured from the four corners of the Internet. It returns only
the records that the nameserver happens to know are associated with a
particular name at a certain point in time. The fact that an MX record is
missing from an ANY query and is then available a moment later in response to
an explicit MX record query therefore doesn't provide much useful diagnostic
information, since the MX query is more rigorous than the ANY query.

> I think there is some problem with the Refresh time and TTL interval.
> Here is my config:
>                 10800                   ; Refresh after 3 hours
>                 3600                    ; Retry after 1 hour
>                 604800                  ; Expire after 1 week
>                 86400 )                 ; Minimum TTL of 1 day

I'm sorry, but I think you have a fundamental misunderstanding here. Those
values only control certain parameters of *your* domain; they have absolutely
no effect on your nameserver's ability to resolve MX records in anyone *else*'s
domain.

> Can anyone tell me what is the problem with my name server?

There may be nothing wrong with *your* nameserver at all. Why don't you provide
some specifics about the domains you're having problems with? Maybe *their*
DNS is screwed up. Won't know until I look.


- Kevin