... or, "Almost a Reverse DNS FAQ"
Reverse DNS turns an IP address into a hostname -- for example, it might turn 192.0.2.25 into host.example.com.

For your domains, standard DNS (turning a hostname into an IP address, such as turning host.example.com into 192.0.2.25) starts with the company (registrar) that you registered your domains with. You let them know what DNS servers are responsible for your domain names, and the registrar sends this information to the root servers (technically, the parent servers for your TLD). Then, anyone in the world can access your domains, and you can send them to any IP addresses you want. You have full control over your domains, and can send people to any IPs (whether or not you have control over those IPs, although you should have permission to send them to IPs that are not yours).

Reverse DNS uses a similar method. For your IPs, reverse DNS (turning 192.0.2.25 back into host.example.com) starts with your ISP (or whoever told you what your IP addresses are). You let them know what DNS servers are responsible for the reverse DNS entries for your IPs (or, they can enter the reverse DNS entries on their DNS servers), and your ISP gives this information out when their DNS servers get queried for your reverse DNS entries. Then, anyone in the world can look up the reverse DNS entries for your IPs, and you can return any hostnames you want (whether or not you have control over those domains, although you should have permission to point them to hostnames that are not on your domains).

So for both standard DNS and reverse DNS, there are two steps: [1] You need DNS servers, and [2] You need to tell the right company (your registrar for standard DNS lookups, or your ISP for reverse DNS lookups) where your DNS servers are located. Without Step 2, nobody will be able to reach your DNS servers.

If you can comprehend the above paragraphs (which takes some time), you'll understand the biggest problem that people have with reverse DNS entries. The biggest problem people have is that they have DNS servers that work fine with their domains (standard DNS), they add reverse DNS entries to those servers, and it doesn't work. If you understand the above paragraphs, you'll see the problem: If your ISP doesn't know that you have DNS servers to handle the reverse DNS for your IPs, they won't send that information to the root servers, and nobody will even get to your DNS servers for reverse DNS lookups.

Basic Concepts:

    * Reverse DNS turns 192.0.2.25 into host.example.com (an IP address into a host name).
    * Typical reverse DNS lookup path: DNS resolver => root servers => ARIN (North American IP registry) => Local ISP => Acme Inc. DNS servers.
    * Whoever supplies your IP addresses (usually your ISP) MUST either [1] set up your reverse DNS entries on their DNS servers, or [2] "delegate authority" for your reverse DNS entries to your DNS servers.
    * Reverse DNS entries use a host name with a reversed IP address with ".in-addr.arpa" added to it -- for example, "25.2.0.192.in-addr.arpa" (".ip6.arpa" is used for IPv6 reverse DNS lookups).
    * Reverse DNS entries are set up with PTR records (whereas standard DNS uses A records), which look like "25.2.0.192.in-addr.arpa. PTR host.example.com" (whereas standard DNS would look like "host.example.com. A 192.0.2.25").
    * All Internet hosts should have a reverse DNS entry (see RFC1912 section 2.1).
    * Mail servers with no reverse DNS will have a hard time getting mail to certain large ISPs.

Very Common Myth:

    * Myth: If you have a reverse DNS entry listed in your DNS server, you have reverse DNS properly set up.
      Fact: This is often not the case. You need TWO things in order to have your DNS set up properly:
          o 1. Your DNS servers (or your ISP's) MUST have the reverse DNS entries set up ("25.2.0.192.in-addr.arpa. PTR host.example.com").
          o 2. AND your ISP or bandwidth provider MUST set up the reverse DNS on their end, so that DNS resolvers around the world will know that your DNS servers are the ones to go to when looking up the reverse DNS for your IP addresses.

How a reverse DNS lookup is accomplished:

    * The DNS resolver reverses the IP, and adds it to ".in-addr.arpa" (or ".ip6.arpa" for IPv6 lookups), turning 192.0.2.25 into 25.2.0.192.in-addr.arpa.
    * The DNS resolver then looks up the PTR record for 25.2.0.192.in-addr.arpa.
          o The DNS resolver asks the root servers for the PTR record for 25.2.0.192.in-addr.arpa.
          o The root servers refer the DNS resolver to the DNS servers in charge of the Class A range (192.in-addr.arpa, which covers all IPs that begin with 192).
          o In almost all cases, the root servers will refer the DNS resolver to a "RIR" ("Regional Internet Registry"). These are the organizations that allocate IPs. In general, ARIN handles North American IPs, APNIC handles Asian-Pacific IPs, and RIPE handles European IPs.

          o The DNS resolver will ask the ARIN DNS servers for the PTR record for 25.2.0.192.in-addr.arpa.
          o The ARIN DNS servers will refer the DNS resolver to the DNS servers of the organization that was originally given the IP range. These are usually the DNS servers of your ISP, or their bandwidth provider.

          o The DNS resolver will ask the ISP's DNS servers for the PTR record for 25.2.0.192.in-addr.arpa.
          o The ISP's DNS servers will refer the DNS resolver to the organization's DNS servers.

          o The DNS resolver will ask the organization's DNS servers for the PTR record for 25.2.0.192.in-addr.arpa.
          o The organization's DNS servers will respond with "host.example.com".

Mail Server Test Center

Manage and monitor email with greater safety and reliability

DNSstuff’s Mail Server Test Center offers powerful tools save you time and headaches when troubleshooting email issues. You simply need to enter your email address and the application finds the MX records for you. You then select the test sand IPs you wish to run those tests against. Result output is presented in a simple dashboard.

Critical real-time tests in one easy-to-interpret dashboard

Mail Server Test Center dashboard

Online real-time reporting

Each RBLalert from DNSstuff.com includes a timestamp of the notice, the name of the blacklist, and instructions or recommendations for removal if necessary. Measured performance and history knowledge is saved in your management screen.

Ensure proper configuration

Incorrect settings and configuration put companies at risk for downtime and improperly routed email; which can negatively impact a company’s brand, customer relationships and revenues.

 

Also included in Mail Server Test Center:

Email Path Analyzer

Email Path Analyzer is easy to use and delivers clear, detailed header analysis all in one comprehensive report.  Now you can deal with troublesome emails with ease.  The time savings alone make this a highly valuable addition to your current DNSstuff Professional Toolset

Email Path Analyzer dashboard

Anti-Virus Filtering Test

This test sends a series of emails to the address you provide. These emails contain the EICAR anti-virus test signature encapsulated in a variety of containers such as an .EXE file, a .BIN file, and a zipped .EXE file.

If you receive any or all of these emails with the attachments intact, contact your email administrator.

It is possible you will not receive the emails at all, if your anti-virus software or email server are properly rejecting infected emails, or emails with certain types of attachments.

"As an email administrator I think your product / service mix is the best.  I recommend it to anyone I train as a must have tool."

Brian Connelly, WorkGroup Associates Inc

Recent Changes to the DNSstuff.com Email Path Analyzer:

Version 1.0.0 08-31-2009

  • Added World Map to help identify and locate From IP's
  • Fixed formatting Issues
  • Fixed whois results to account for missing results
  • Added additional parsing to handle Postini mail Servers.
  • Updated Threat Level filters to account for additional scenarios.

Version 0.0.6 08-19-2009

  • Added tool tips to the summary section describing each value.
  • Changed IP Address to From IP on delivery path page.
  • Added x-mimeole to the client / device description.
  • Fixed formatting Issues
  • Added WHOIS data to the delivery path page (Note: some whois listings are unavailable and an update is underway for our next release)
  • Updated Threat Level filters to account for additional scenarios.

 

Version 0.0.5 08-14-2009

  • New Enhanced Error Messages
  • Updated Delivery Path Page by adding Time Zones information and Improving parsing of IP Addresses
  • Added additional formating to the header input to to allow for the rendering of special characters.
  • Updated Threat Level filters to account for additional scenerios.

Version 0.0.4 08-12-2009

  • Reversed delivery path received lines so that sender is at the top
  • Formatting enhancements

Version 0.0.3 08-11-2009

  • Updated Threat Level filters to account for additional scenarios

Version 0.0.2 08-07-2009

  • Received lines that started with a 127.0.0.1 address as the first received in an Email chain were not being processing. They process now, but leave the 127.0.0.1 as the Source IP. An additional fix for this source IP will be in place shortly (next real IP address in the chain will be used for analysis).
  • An update to the Test ID has been added and is visible on the tool for support references.
  • Updates to the feedback path and our surveys have occurred.
  • Additional internal error checking has been added.

Version 0.0.1 08-06-2009

  • Initial launch: Please send feedback to This email address is being protected from spambots. You need JavaScript enabled to view it.

Recent Changes to the DNSstuff.com Mail Server Test Center Beta:

Version 1.0.15 02-Aug-2009

  • Warning message if an MX record does not resolve to an address.

Version 1.0.14 31-Aug-2009

  • Moved CAPTCHA image out of Joomla to increase perfomance.
  • Removed all digits from CAPTCHA.
  • Increased CAPTCHA length from six to eight characters.

Version 1.0.13 31-Aug-2009

  • Updated link to this article

Version 1.0.12 31-Aug-2009

  • First revision out of beta

Version 1.0.11 27-Aug-2009

  • Updated CAPTCHA popup to not flicker/scroll the screen when opening for Anti-Virus and Anti-Spam tests
  • Anti-Virus compressed test files (.ZIP, .GZ) fixed.
  • Added email to Anti-Virus and Anti-Spam test to tell people what to watch for as positive confirmation that the test was run and is emailing properly.

Version 1.0.10 26-Aug-2009

  • Added help buttons for Anti-Virus and Anti-Spam tests.
  • Added delivery status to Anti-Virus and Anti-Spam popups post-CAPTCHA.
  • Refactored dashboard AJAX calls to direct model.
  • Raised number of outstanding AJAX requests in dashboard back to four.

Version 1.0.9 26-Aug-2009

  • Reduced complexity of CAPTCHA image.

Version 1.0.8 26-Aug-2009

  • Added username tagging to Anti-Virus and Anti-Spam tools to help curb abuse.

Version 1.0.7 Unreleased

Version 1.0.6 Unreleased

Version 1.0.5 24-Aug-2009

  • Help links changed to jQuery dialog.
  • Integration of Anti-Spam and Anti-Virus tests.
  • Many look and feel enhancements.
  • Email Path Analyzer tool link.
  • Integrated with new Spam Database Lookup Tool.

Version 1.0.4 13-Aug-2009

  • UI enhancements.  Help div animated, help text corrected.

Version 1.0.3 12-Aug-2009

  • Help buttons active, open in a hidden div.

Version 1.0.2 12-Aug-2009

  • Open Spam Database Lookup and IP Information links in new window.

Version 1.0.1 12-Aug-2009

  • Status indication on what is currently running and when the tool is finished.

Version 1.0.0 12-Aug-2009

  • Initial launch: Please send feedback to This email address is being protected from spambots. You need JavaScript enabled to view it.

RBLalerts: Email Blacklist monitoring around-the-clock

Avoid irreparable harm to both reputation and commerce
DNSstuff.com's RBLalert service eliminates concerns over unanticipated IP blacklisting, downtime and chances of financial harm due to email disruption. DNSstuff offers a proactive monitoring service called RBLalerts that informs you about the status of your mail server IP. We query your IP against the industry's most popular SPAM databases 24/7/365. You will receive an email alert when you have been listed or delisted from a SPAM blacklist. RBLalerts notify you before your business is at risk.

Simple setup, configuration and management

This service requires only an IP address to monitor and an email address for notification. You have the ability to easily enable/disable alerts through management interface.

Set up new alert with RBLalertclick to zoom

Detailed query to over 50 feeds (70+ blacklists)

DNSstuff queries your mail server IP against the most trusted blacklists available.

Online reporting

Each RBLalert from DNSstuff.com includes a timestamp of the notice, the name of the blacklist, and instructions or recommendations for removal if necessary. Measured performance and history knowledge is saved in your management screen.

RBLalert Dashboardclick to zoom

RBLalert sent via plain text email

A simple text based email will arrive immediately when your mail server IP has been listed or delisted from a blacklist.

Customized Plain Text Alerts
click to zoom

Insight on removal and resolution

Each RBLalert from DNSstuff.com includes a timestamp of the notice, the name of the blacklist, and instructions/links or recommendations for removal if necessary.