The Internet is hard.

There are so many things that need to happen to make the Internet work. DNS entries need to be right. MXs need to be set up. Web servers need to be configured. And, let’s be honest, anyone who has ever run their own services on the Internet has flubbed a configuration.
We don’t think about it, because most of the time the configurations are handled by scripts and they do things right. But at some point someone needs to type in something and there’s a risk it will go horribly wrong. I’ve been digging into domain data for a client of mine today. I think I’m going cross-eyed over it. But I have found so many weird things that just mean someone isn’t paying attention to what they’re doing.
Like the domain that has a MX record that says:
nullmx
 
I’m pretty sure the intention of the domain owner is to publish a null MX. But they added an extraneous “0” in there and ended up publishing something really weird. Even worse, the MTA that this client is using is listing this as a “delivered” email. I’m pretty sure that mail to that domain never left the MTA.
I’ve found horribly typoed MX domains for popular spam filters. I’ve found domains that have invalid characters in them. I’ve found domains that are totally a mess.
The vast majority of us have some story or other of the time we really broke things by accident. Like the time a very large ISP deleted their MX records. Or when a different ISP changed their internal forwarding and broke SPF authentication for everyone mailing that domain. Or when another ISP accidentally blocked every IP beginning with 6.
Sometimes I’m amazed that the Internet ever works. No matter how big it gets, there are actual people writing actual code and configurations. The number of things that have to happen to get packets from A to B is pretty impressive. We rarely ever notice the breakages, the people who run things are really good at their jobs. But sometimes poking in the grotty corners reminds me how easy it is to break things. It’s sometimes a wonder things actually work.
 

The 10 worst …
Email nightmare for some FSU students

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The long tail of domains

I frequently get clients telling me that they have about 15 (20, 30) major domains on their list, and then a long tail of domains with only a couple of recipients. If you sort simply by the left hand side of the @, that’s true.
When you’re sending email, it’s not just the domain in the email address that is important. Of equal importance is the MX. The MX is what actually handles the mail and where many filters are applied. Sorting by MX, instead of simply recipient domain, can identify that most of your small business clients are hosted at a particular provider. The number of subscribers behind that filter may be enough to push that filter into your top 10 or even top 5 recipient domains.
There’s a much smaller tail when grouping recipients by MX domain. It makes it much easier to understand where blocks are happening. I have even seen cases where clients didn’t realize they were blocked at a commercial provider because they only saw the “onesie twosie” domains as undeliverable. They missed a real problem with blocking because they were looking at the wrong data.
I sometimes get the side eye from some ISP folks if I use the term receiver (because, well, they’re senders as much as they are receivers). But I use receiver to help distinguish between the recipient domain and the actual domain handling the email.
When was the last time you looked at your delivery by filter or MX rather than by recipient domain? What did you find?

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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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TXTing

txt
On Friday I talked a bit about the history behind TXT records, their uses and abuses.
But what’s in a TXT record? How is it used? When and where should you use them?
Here’s what you get if you query for the TXT records for exacttarget.com from a unix or OS X command line with dig exacttarget.com txt

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