nanog mailing list archives
Re: DNS question, null MX records
From: Mark Andrews <marka () isc org>
Date: Wed, 16 Dec 2009 13:58:56 +1100
In message <4B284376.3000800 () mail-abuse org>, Douglas Otis writes:
On 12/15/09 8:06 AM, Andy Davidson wrote:Eric J Esslinger wrote:I have a domain that exists solely to cname A records to another domain'swebsites.[...]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...SRV records documented the hostname "." as representing "no service". However, errors made by non-RFC-compliant clients still generate a fair amount of root traffic attempting to resolve A records for ".". The MX record never defined a hostname "." to mean "no service" so it would be unwise to expect email clients will interpret this as a special case meaning "no service" as well. One might instead consider using: example.com. IN MX 0 192.0.2.0 IN MX 10 192.0.2.1 ... IN MX 90 192.0.2.9
Which will expand to: example.com. IN MX 0 192.0.2.0.example.com. IN MX 10 192.0.2.1.example.com. .... IN MX 90 192.0.2.9.example.com. MX records DO NOT take IP addresses.
where 192.0.2.0/24 represents a TEST-NET block. This should ensure traffic will not hit the roots or your servers. Assuming a sender tries all of MX addresses listed, they may still attempt to resolve A records for example.com. This MX approach will affect those failing to validate email prior to acceptance, and, of course, spammers. -Doug
-- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: marka () isc org
Current thread:
- Re: DNS question, null MX records, (continued)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- Re: DNS question, null MX records Mark Andrews (Dec 16)
- RE: DNS question, null MX records Brian Dickson (Dec 16)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 15)
- Re: DNS question, null MX records Mark Andrews (Dec 15)
- Re: DNS question, null MX records Tony Finch (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Joe Abley (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Paul Vixie (Dec 16)
- Re: DNS question, null MX records Douglas Otis (Dec 16)
- Re: DNS question, null MX records Paul Vixie (Dec 16)
- RE: DNS question, null MX records Jay Mitchell (Dec 18)