HE.net DNS problems

Hurricane Electric had a significant outage of their authoritative DNS servers this morning, causing them to return valid responses with no results for all(?) queries. This will have caused delivery problems for any mail going to domains using HE.net DNS – which will include some of their colocation customers, as well as users of their free services – but also will have caused reverse DNS to fail for most servers hosted by Hurricane Electric worldwide, so if any of your mail is being sent from HE hosted machines you may have seen problems.
(We’re HE customers so we noticed. Still happy with them as a vendor.)

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SPF: The rule of ten

Some mechanisms and modifiers (collectively, “terms”) cause DNS queries at the time of evaluation, and some do not. The following terms cause DNS queries: the “include”, “a”, “mx”, “ptr”, and “exists” mechanisms, and the “redirect” modifier. SPF implementations MUST limit the total number of those terms to 10 during SPF evaluation, to avoid unreasonable load on the DNS. If this limit is exceeded, the implementation MUST return “permerror”.

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PTR Records

PTR records are easy to over look and they have a significant impact on your ability to deliver mail without them.  Some ISP and mailbox providers will reject mail from IP addresses that do not have a PTR record created. PTR records are a type of DNS record that resolves an IP address to a fully qualified domain name or FQDN.  The PTR records are also called Reverse DNS records. If you are sending mail on a shared IP address, you’ll want to check to make sure the PTR record is setup, however you most likely will not be able to change it.  If you are on a dedicated IP address or using a hosting provider like Rackspace or Amazon AWS, you’ll want to create or change the PTR records to reflect your domain name.
We usually think about DNS records resolving a domain name such as www.wordtothewise.com to an IP address.  A query for www.wordtothewise.com is sent to a DNS server and the server checks for a matching record and returns the IP address of 184.105.179.167.  The A record for www is stored within the zone file for wordtothewise.com.  PTR records are not stored within your domain zonefile, they are stored in a zonefile usually managed by your service provider or network provider.
Some service providers provide an interface where you can create the PTR record yourself, others require you to submit a support request to create or change the PTR record.
If you know what IP address you are sending mail from, use our web based DNS tool to check if you have a PTR record created.
http://tools.wordtothewise.com/dns
Checking for a PTR record for 184.105.179.167 returns
167.128-25.179.105.184.in-addr.arpa 3600 PTR webprod.wordtothewise.com.
If you received Response: NXDOMAIN (There is no record of any type for x.x.x.x.in-addr.arpa), this means you’re missing the PTR record and need to create one ASAP if you are sending mail from that IP address!

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