DANE plus wildcard record

Rob McGee rob0 at nodns4.us
Sat Jun 15 20:48:27 CEST 2019

On 2019-06-15 12:11, I wrote:
> One of my subscribers recently signed his or her zone, and sadly, has a
> wildcard A in that zone.  Unfortunately at this point I do have to keep
> that zone name private, although offlist I'd tell it to someone I know
> and consider trustworthy to maintain the user's confidence.

The immediate problem has been solved with a bandaid,
smtp_tls_policy_maps, with an entry:

example.com    may

This overrides the global "smtp_tls_security_level = dane" setting, and
I've confirmed that I can send mail to the subscriber now.

> Oh, if you consult your dane.sys4.de logs for a bit ago, I suppose I
> already DID tell you the zone name. :)  Starts with "a" and is in com.
> TLD.  The checker reports "DNS lookup error for TLSA records: 
> which is what I get on the named recursive resolver that Postfix is
> using, querying "_25._tcp.smtp.example.com./IN/TLSA".
> So Postfix is refusing to deliver, believing that there should be a
> TLSA.  But AFAIK this user never published TLSA.
> The SOA MNAME host has disabled version.bind./CH/TXT lookups so I am
> not sure what software is in use, but having A for an invalid hostname
> (underscores not allowed in hostnames) would be a problem for BIND
> named, which by default would not allow that.  But I don't know how
> that feature interacts with wildcard records.
> Testing on a dnsmasq from home I don't get SERVFAIL, just NOERROR.

I still think this is an interesting problem, perhaps a BIND problem.
The user didn't set a TLSA and might have had no idea about DANE ("isn't
that what Hamlet was?") and yet was unable to get mail from my DANE-
enabled host.

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