nanog mailing list archives
Re: DNS question, null MX records
From: Douglas Otis <dotis () mail-abuse org>
Date: Tue, 15 Dec 2009 18:18:30 -0800
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'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...
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 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
Current thread:
- Re: DNS question, null MX records, (continued)
- Re: DNS question, null MX records Daniel Senie (Dec 15)
- 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)