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The Do's & Don'ts of Naming Your IP Addresses

David Harris
by David Harris on October 11, 2017

Naming Your IP Addresses

What's in a Name?

As humans, we love to name things: children, pets, streets, mountains, rivers, oceans, deserts, and IP addresses. Yes, IP addresses. If you're running an email server, then each of your IPs needs a name. But you need to choose that name wisely, because choosing the wrong name (or not setting it up correctly) can affect your email deliverability.

Thankfully, you don't need to be super-creative or spend hours pouring through baby name books. Just follow a few simple guidelines (listed conveniently below) and you should be well on your way towards choosing the perfect name for your babies... I mean, IP addresses. :-)

Choosing a Name (Hint: Keep it Simple)

While there's no such thing as a "wrong" name, it's certainly possible to choose names that hurt your deliverability or create more setup hassles than they're worth. Here are four things to keep in mind when naming your IPs:

1) Use a sub-domain of your server name

Your IP addresses should use a sub-domain of the domain name of your server. For example, if your server is "mailer.example.com" then name your IP addresses something like "smtp1.mailer.example.com", "smtp2.mailer.example.com", etc. Having this sub-domain relationship makes setting up feedback loops much easier.

It's an easy pitfall to think you need multiple domain names for multiple IP addresses. For example: "smtp1.brand-a.com", "smtp2.brand-b.com" and "smtp3.brand-c.com. But it's not a good idea. And it can hurt your email deliverability because it looks like a technique called "domain snow-shoeing" that spammers use (where they try to look like multiple companies.) For more details on how many IP addresses you need, see our post on Multiple IP Addresses: Why and How Many?

2) Almost nobody will see these names

Your subscribers are not going to see these names. Only people reading through email headers and anti-spam analysts will see them. So there are no extra points for creativity here. Boring and generic is great for this!  (Save your creative juices for your email content and offers.)

3) Don't look like a dynamic IP address

Dynamic IP addresses are assigned as neededevery time a device connects to the network it gets assigned a new IP address. For example, right now my home router's IP is 173.18.105.63, but tomorrow it could be different if my router reboots and has to get a new IP.

These dynamic IP addresses often have specific patterns in their names. For example, the corresponding name of my home router's IP is "173-18-105-62.client.mchsi.com". Notice how the entire IP address is actually part of the name. This is a dead giveaway of a dynamic IP address.

This matters to you as an email sender because a lot of spam is sent from dynamic IP addresses. Naturally, IPs that are dynamic or have dynamic looking names will have delivery problems.

Here is how to NOT look like a dynamic IP address:

  • Do not have all of the numbers of your IP in the name. For example, 11-22-33-44.mailer.example.com would be bad for the IP 11.22.33.44. Most dynamic IP addresses look like this.
  • Do not have the last number of the IP in the name. For example, smtp44.mailer.example.com is bad for the IP 11.22.33.44. We've seen this cause email to be rejected.
  • Do not use the words "pool", "dhcp" or "dyn" in the name.

4) Count in order

Our recommendation is to use names with a clear counting order (like "out1", "out2", "out3", etc or "smtp1", "smtp2", "smtp3", etc) followed by your server's domain name.

Remember we said that the IP address names should not include the last number of the IP address? If your IP addresses are sequential, then start counting at any number other than the last number in your first IP address. For example, if your first two IPs are 11.22.33.44 and 11.22.33.45, then they could be named smtp1.mailer.example.com and smtp2.mailer.example.com—but not smtp44.mailer.example.com and smtp45.mailer.example.com. This helps keep your IPs recognizable while ensuring the best deliverability possible.

Getting Your New IP Names Ready to Send

Now that you have decided on the names of your IP addresses, there are five more things you must do before you can let your babies leave the nest and start sending email:

1) Configure Forward DNS

The Domain Name System (DNS) is how the Internet translates from human-readable names to IP addresses. Humans would much rather type www.google.com instead of 108.177.112.147 into our web-browsers. You can think of DNS as the phonebook of the Internet translating names into numbers.

Each of your IP addresses needs to have an "A" record that associates the name with the IP address (this is known as Forward DNS )You can set this up via your domain name registrar, DNS hosting service, or your IT department. Most providers have a simple web interface for setting up Forward DNS records.

2) Configure Reverse DNS

The DNS system also has a "reverse" method that can translate IP addresses back into names. This is called, you guessed it Reverse DNS! Sending email requires that each IP address has Reverse DNS working.

You will set up Reverse DNS with whoever provided your IP addresses: typically either your dedicated server provider, your bandwidth provider, or your IT department. Many dedicated server providers have a way to configure this directly in their customer management console, but sometimes you have to open a support ticket.

Before you setup Reverse DNS, make sure that your Forward DNS is set up properly. Many providers will refuse to set up the Reverse DNS until the matching Forward DNS is in place.

3) Configure your software

Did you know that when sending an email through SMTP, before sending the actual email message, the servers say "hello" to each other and exchange their names? (Well, actually "HELO" or "EHLO" because they are computers, but it's still quite friendly and cordial.)

And in order to be polite, your email server needs to know its own name. If I try to greet someone with an obviously fraudulent name, people are likely to look at me askance and distrust what I have to say. Likewise, if a server says "hello" using a name that does not match the Reverse DNS name of the IP address, then many email providers will slam the door and not accept any email. If you're using GreenArrow, just configure the name of each IP address in the "Hostname" setting of the IP address and you're all set!

4) Register for feedback loops

Email feedback loops are used by ISPs to notify senders when their subscribers mark emails as being spam. They're valuable both from a statistical standpoint and because they enable you to stop sending to subscribers who generate spam complaints.

The registration process for most feedback loops includes registering all of your sending IPs, so it's important to update your registrations any time you're adding or renaming IPs.

5) Update SPF and Sender ID records

SPF and Sender ID are two forms of email authentication which can be used to authorize IP addresses to send email for a domain. The main differences between SPF and Sender ID are that SPF is more widely supported and is only used to authenticate the Return-Path domain, while Sender ID can also be used to authenticate the From or Sender header domain.

If you're a GreenArrow Cloud customer, these five steps are taken care of because you'll be using our configured email delivery servers. For those considering our On-Premises solution, we'll guide you through all of the details of choosing how many IPs you need, setting up the IP addresses including Forward DNS, Reverse DNS, feedback loops, and warming up your IP addresses as part of our LaunchAssist package

They Grow Up So Fast...

And that about wraps it up. As long as you follow these guidelines, your newly named IP addresses should be ready to start sending email in no time. 

Let me know in the comments if you have any questions (or want to share names you gave your IP addresses). And of course, if you need help with software or have a deliverability question, we're always here and happy to help. Until next time, happy sending!

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Multiple IP Addresses: Why & How Many?

A popular question is answered in our free eBook! How many IP addresses does your business need? Our team reviews how volume, budget and reputation matter—giving you the tools for your business and budget.

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David Harris
Written by David Harris
David first started his own business when he was still in high school. DRH Internet, Inc. began as a web hosting company, but as David's consulting experience grew, he found himself working frequently with open source email servers and writing custom software to solve problems. Over time his software grew into a full-fledged email platform called—you guessed it—GreenArrrow. In his spare time, you can usually find him taking classical guitar lessons, drinking gourmet coffee, playing Go, and spending time with his wife Penni and their four amazing children.

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