DNS question, null MX records

Andy Davidson andy at nosignal.org
Tue Dec 15 10:06:15 CST 2009

Eric J Esslinger wrote:
> I have a domain that exists solely to cname A records to another domain's websites.
> I found a reference to a null MX proposal, constructed so:
> example.com    IN    MX 0 .
> Question: Is this a valid dns construct or did the proposal die?

It's "valid", but you will probably find people still try to spam to
machines on the A records, and all of the other weird and wonderful things
that spambots try to do to find a path that will deliver mail...

If there is no time that mail should appear *from* this domain name then
it's polite to set spf records as such - one of the few things spf is
always useful for :-) like this :

@	IN	TXT	"v=spf1 -all"

... all this means in practice though is that spammers who actually bother
to check for this, will find someone else to masquerade.  But you won't
have to deal with the associated attempted bounce delivery connections...

Best wishes

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