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What is Email Deliverability?

In a nutshell, it’s the difference between people receiving your emails and not receiving them.

Who is this Ultimate Guide for?

  • You are someone who sends emails and your job (sales) depends on people receiving them. 
  • Not only do you want people to get them, but you want them to be read as well.
  • You really don’t want your emails bouncing, being undelivered, or ending up in the junk.
  • And you want an easy to follow guide to maximise your chances.

Purpose of the Ultimate Guide

To put it simply: To show you best practise etiquette for everything you need to know, and do, to make sure your emails serve you as well as you need them to.

Chef putting pizzas in to a pizza oven
Throughout this guide we’ll be using pizza based analogies that we’ve highlighted in green.

Stick with us on this one – as it’s an analogy that keeps on giving, and let’s be honest, everyone can relate to pizza!

Pizza Takeaway Analogy

– Your pizza oven needs to be working

– You need to have decent, fresh ingredients

– Your delivery drivers need to be fit and well

– Your delivery vehicles need to be in reliable working order

– Your customer needs to provide you with an address to deliver the pizza

If any of these things aren’t right, then the pizza either doesn’t arrive with the customer or the customer sends it back and doesn’t bother ordering from you again.

Well, same with your emails. Get your content and your delivery mechanisms in tip top shape and everyone’s a winner.

Good luck! 

If you need any help, have any questions, or aren’t sure about any of it, please don’t hesitate to drop me a line on esther@kulea.ma

We have included a Useful Links section at the end of this guide

Your IP is an address unique to the servers sending your emails, and you want to keep it squeaky clean

1. IP Reputation

What is IP Reputation?

IP (Internet Protocol) is like an address – it uniquely identifies, in a string of numbers, the computer server that is sending out your emails.

Email Service Providers (ESPs) like Google and Hotmail can check the IP address of an email sender and do a check on the reputation of that IP. Think of it like a credit score for your email trustworthiness.

Why and how to protect your IP Reputation

If you get a bad IP rep, Google doesn’t want to know, thank you very much *puts email in junk*. 

You serve up enough inedible pizzas and then try and deliver a pizza, it’s going in the bin instead of on the plate, right?

IP rep needs to be protected so that ESPs don’t divert your emails in to junk folders.

You can send your emails from a reputable and dedicated IP address that is clean and tidy and passes health checks. See: The IPs that Kulea uses to send out emails are in tip top shape.

What not to do

You don’t let any old random person drive your car, do you? Who knows what kind of a state it will be in when they hand the keys back. 

Same goes for your IP. 

It is possible to share IP addresses with other domains but you can’t be sure of your IPs reliability if any old random domain is sharing with you. Basically, if they send out a spammy email about cheap viagra, they’ll take you down with them.

So. Keep clear of shared IPs. Use dedicated ones like Kulea does when sending out emails, or at the very least, keep a really close eye on your domain reputation using third party tools like Senderscore (see video below) 

Kulea is dedicated to IP reliability

Kulea uses experts in deliverability, Mailgun, to deliver emails out for all of our customers. They are sent from dedicated IP addresses which, as we block campaigns that have a higher than 5% bounce rate (it’s tough love, we know, but you’ll thank us for it later), are flawless when it comes to IP reputation . We also follow all the best practice contained in this guide, so rest assured you’re in good hands.

Because we look after our IPs really really well, our customers have peace of mind knowing that their emails are being sent from a protected IP with a good rep. 

Our sender scores don’t go below 99% – not bad, eh?


  • Help us look after our IPs by looking after your domain rep
  • Check the health of your IP  
  • Check out the Useful Links section below

Tutorial: Use Senderscore to check the reputation of an IP

2. Domain Reputation

What is Domain Reputation?

Your Domain Name is the human language translation of the numbers that make up your IP address. As mentioned, and best avoided, more than one domain can live on a shared IP.

In the same way that IPs have a reputation that needs protecting, so too does every domain. 

In the same way that Google and Hotmail work hard to do right by their clients and chuck spammy emails from dodgy IPs in the junk, so they assiduously check on sender domains as well.

Nobody likes being spammed so you’re probably grateful to your ESP for being on the ball about this stuff, but they don’t do it alone. The lovely folk at Spamhaus, Apache, Barracuda (this is just a handful of examples, not a comprehensive list) also work behind the scenes developing spam blacklists to spare you from spam. For a full list of blacklist providers and to see whether your domain is featured, visit mxtoolbox.com/blacklists.aspx.

Domains that are well established and have been sending emails for a while, have reputations – hopefully good ones.

Domains that are brand new, and that aren’t recognised by ESPs, don’t have any reputation and will be treated with caution: When there’s no credit history, there’s no easy way to get credit. 

Why and how to protect your Domain Reputation

If you don’t protect your domain reputation, ESPs and other spam checkers will just start diverting your emails (including the ones you send to your Mum) directly to the junk box. When this happens your emails won’t get opened, emails that don’t get opened don’t get replied to and reflect badly on your domain, and eventually your domain ends up in a downward spiral of reputational damage.

If you set up your domain name properly by adding records to the Domain Name System (DNS) that verify the authenticity of your emails, ESPs will treat you nicer.

See Tech Set-up for a better understanding of the records that Kulea can help you add to your DNS.

If you follow email marketing best practices as well, then your domain rep should stay in good shape. However, if you have a reputational mishap, all is not lost, as domain reputation can be rebuilt over time – see kulea.ma/marketing-best-practice/why-do-my-email-open-rates-suck.

Also see Data Quality and Email Content for best practice guidance.

What not to do

Don’t risk tarnishing your domain reputation by sending emails to poor quality data (people who don’t open, who unsubscribe, or who complain), or by sending poor quality content.

Don’t send awful pizzas, don’t send them to people who didn’t ask for it or won’t open the door, don’t send them to people whose card was declined, and don’t send them to people who no longer live at the delivery address they gave you.

Kulea – the experts in domain Hygiene

Because Kulea sends out emails through Mailgun, our customers’ domain reps are kept clean as a whistle, giving you peace of mind that your domain rep is being protected by experts. Health checks and troubleshooting are part of the service too.

Check out our blog for useful tips on best practice email deliverability.


For a new domain (or a new sub-domain), warm-up your domain reputation by sending regulated volumes of emails to contacts you know are going to open them and gradually increase volumes.

Use subdomains as they can recover from a tarnished reputation by being replaced, or being gently eased back through another warm-up phase if needed.

Check out the Useful Links section below

Tutorial: Use mxtoolbox to check your domain and ensure the right records are on your DNS

Domain verification is the backbone of your deliverability strategy


3. Tech Set-up

Why and How to

Without wishing to sound too obvious about it, the technical machinations that happen in the background of email sending and receiving are vital for sending and receiving emails.

First things first: Make sure you have the right DNS (Domain Name System) settings for your domain. A bunch of acronyms follow. Do not be afraid. We got this.

You will need to add these to your DNS records by logging in to your domain hosting provider e.g. Godaddy, 123-reg, Hostgator, or Gandi (again, a handful of examples, not an exhaustive list):

If a domain has MX records, it means it receives emails, which means it’s not just broadcasting without receiving (which is not a great practice).

MX = Mail Exchange

This is about receiving emails. A lot of the time, clever integrations between a DNS provider and an ESP mean that your MX records get automatically added to your DNS. 

SPF = Sender Policy Framework 

This specifies a list of authorised IP addresses or providers that can send email for a given domain.

Having a valid SPF record in place is absolutely essential to sending emails. It’s your way of publicly declaring that you’re okay for your email client to send out your emails on your behalf, and it weeds out spammers and phishers that are trying to send out emails using your domain without your permission.

Your SPF should be added as a TXT record (weirdly, not as an SPF record – they’re no longer valid) to your DNS as a publicly visible record. Our Kulea SPF, for example, looks like this:

v=spf1 include:eu.mailgun.org include:_mailcust.gandi.net ~all

Translating this into English, we can see that the first part (v=spf1) is simply us stating which SPF version we’re using (we’re using version 1).

The second part (include:eu.mailgun.org include:_mailcust.gandi.net) is us publicly vouching for Mailgun and Gandi (our hosting provider) to send emails on our behalf, and the final part (~all), simply states that all checks should meet these conditions. If they don’t, then they will fail.

That’s a really simple overview of SPF, however, we recommend reading deeper on the subject as there really is quite a bit to cover and it’s pretty important. A great starting point is pair.com/support/kb/what-is-an-spf.

DKIM = DomainKeys Identified Mail

Adding this record to your DNS is like signing your emails. It verifies to the recipient that a message was sent from a legitimate user of an email address. It’s a digital signature added to your email header that is unique to your domain.

Unlike SPF, DKIM uses encryption to provide an additional layer of security and we always recommend adding both SPF AND DKIM. See dmarcanalyzer.com/dkim for history and more info on DKIM.

Kulea helps all of our customers through this bit by providing the right info for the records. All you have to do is login to your DNS provider, go to DNS records, and do a copy/paste.

DMARC = Domain-based Message Authentication, Reporting & Conformance (mouthful!!)

This is newer. 

DMARC sits on top of your SPF and DKIM to provide a standardised policy that covers how you treat non-verified emails. You can either choose to do nothing (but log the fail), quarantine the email (which directs it to the recipients spam folder), or reject the email completely, which prevents it from ever getting delivered.

DMARC also allows you to register a reporting address where ESP’s can send response logs, allowing you to track the potential abuse of your domain.

If you already have your DKIM and SPF in place, then setting up your DMARC is a relatively easy next step – and one that the ESP’s look out for. Simply jump over to mxtoolbox.com/DMARCRecordGenerator.aspx to set one up.

BIMI = Brand Indicators for Message Identification

This is even newer!

So new in fact, that’s it’s not been widely adopted yet, however it’s coming, and if you’re a brand that wants to gain even greater recognition, then this could be for you.

Simply put, BIMI enables you to attach your logo to all your company emails, so that they show in the side bar of the recipients email client. BIMI is being driven by global players like Google and Yahoo, and works directly with DMARC (If DMARC fails, then the logo won’t appear).

Still in it’s early days, BIMI has yet to gain traction with most ESPs, but it’s only a matter of time so we recommend getting up to speed over at bimigroup.org.


It’s long been considered best practice to separate day to day corporate emails from marketing emails through the use of a sub-domain. I.e. rather than using the email address andrew@acme.com to send marketing emails, you would send using andrew@my.acme.com.

By using a subdomain, you’re protecting your root domain from any reputation damage that might be incurred from your sales and marketing email activity, which is a good thing. However it’s worth noting that as an absolute minimum, if you want to use a subdomain, you will need to add SPF and DKIM records for them to your DNS.

Things to avoid

  • Don’t send emails from your domain and make the “send from” email address different from the sender domain. It smells fishy and ESPs check this stuff.
  • Don’t set up your SPF/DKIM/DMARC without testing that they validate correctly. Use MX Supertool to check everything. Twice!  
  • Having MX records in place is good, but make sure there’s a mailbox at the other end of the line that’s receiving replies to your emails, and that there’s a person manning those replies. The best indicator of a good quality domain is the quality of email conversations taking place through that domain.
Image of a pizza

If you got a pizza delivered and on the outside of the box is the logo for (I don’t know, some very delicious and reputable pizza company) but inside is just another crummy old pizza from RubbishPizzasRUs, you wouldn’t be all that happy either. Deception isn’t cool.

Kulea is here to help! 

Kulea adds your domain to our Mailgun account, allocates an IP address from which your emails are sent, sets up SPF and DKIM records for your DNS and all you have to do is copy and paste them in.


You can find your DNS settings when you login to your domain hosting provider.

Check out the Useful Links section below

4. Data Quality

What is Data Quality?

This is possibly easier to explain by saying that Poor Data Quality = 

  • Email addresses that bounce (they left the company two years ago!)
  • Email addresses that don’t open the email (no-reply@)
  • Email addresses of people who unsubscribe or complain about receiving your email

Best not to send emails to these kinds of email addresses.

Good Data Quality is basically the opposite of that: We’re talking about legitimate contacts (people who actually exist and who check their inbox), people for whom your emails are relevant (your customers, your suppliers), well-targeted, as in emails about pepperoni to pizza restaurants, people who open emails, people who reply/click or otherwise engage with your emails, and above all, people that have told you they want to receive your data (by opting in).

Keeping things above board

Remember back in May 2018, when every mailing list you’d ever signed up to (and forgotten about) got back in touch asking you to opt back in to their mailing list?

GDPR is not exactly straightforward but you want to make sure of these two important things:

  • That the email addresses in your database are are good data: People – real people – who opted in to your mailing list or to receiving emails like the one you’re sending. 
  • That you give them a chance to opt out or unsubscribe in case they, for whatever reason, don’t want to get them any more.

Beware of invalid email addresses and catch all email addresses. They don’t bounce but they are not good data. We are talking about emails addressed to someone who left the company yonks ago but the company has this kind of dumping ground account that lets everything in. It’s not good quality (Check out this article from neverbounce about best ways of weeding them out..)

Unfortunately with the latest Apple IOS email privacy update, emails are as likely to be opened by Apple as they are by the recipient, so you can no longer rely on email opens as a legitimate indicator of recipient engagement.

To keep your data clean, we recommend regularly checking for other signs of engagement, such as clicks, page visits, webinar attendances, and so on. If a contact drops off the radar on these metrics, having previously been engaged, whilst continuing to open emails, it’s likely to be Apple at work – so treat with caution.

What’s the point of all of this?

Because your Domain Reputation depends on it. 

If your emails end up in spam/junk, or bounce, or don’t get opened, they don’t get read, and well, exactly, what’s the point?

What can you do?

Clean your CRM data or contacts spreadsheet by running it through https://app.neverbounce.com/ before you upload it to Kulea. We don’t want you sending emails to addresses that bounce or won’t ever get read, and neither do you. 

The worst offending email addresses for low open rates are those catch-all email accounts.

Kulea encourages you to check the % of catch-alls in your list so that you aren’t risking your reputation on them. When you import your list to Neverbounce, get it cleaned so that you can check for valid emails and catch-alls in the results.

A host of easy tutorials from Neverbounce can be found here.

Then take a good look at who is and who isn’t engaging with your email comms. Give those that aren’t an opportunity to come back into the fold – but if they continue to ignore you, consider cutting them out of your comms.

What not to do

Don’t import email addresses that are not going to be opened by anyone e.g. no-reply@
Don’t import email addresses that haven’t got a clean bill of health from neverbounce

Don’t go out an buy dirty great data lists – use opt in or GDPR compliant legitimate prospected data only

Kulea is an email deliverability specialist

You may have realised this already. 

When Kulea sends emails for you, they very rarely go out to poor quality data and, as these things are part of a fantastic marketing automation solution, if any data needs to be cleaned up (contacts change jobs from time to time) Kulea’s clever automation system keeps things up to date by auto-archiving contacts that bounce, meaning you can’t contact them again.

Like you, Kulea doesn’t want emails to bounce. Because we have lots of customers who enjoy the benefits of sending from IPs with high high high reputation, we have a bounceback threshold of 5%. Any email campaign that hits that bounceback threshold is paused so that the data can be checked and cleaned before resuming.

Tutorial: Using neverbounce to check your database records for bouncy email addresses

5. Email Content

What has this got to do with deliverability?

You have already got a great IP rep, great Domain rep, all the right records on your DNS, and a database full of lovely contacts who subscribed to your newsletter. 

What more could we possibly want?

To be Spared from Spam!

While we don’t open our junk boxes very often, we all know what a junk email looks like: 

FREE OFFER, VIAGRA, and a host of other terms and phrases that stand out a mile.

Email content should be relevant to your recipients, it should be something that interests them, something that they want to read, something that they signed up for when they subscribed to your mailing list.

Best Practice:

Know your audience

Your audiences signed up to your mailing list at a particular event, filled out an online form, opted in from a webinar, and a myriad of other ways … you know something about them already.
Target your emails to suit them. 
To drag an analogy out as much as possible: 

Send your email about great deals on pizza oven fuel to those who work at pizza restaurants and signed up to your mailing list at the pizza oven expo stand.

Image of a slice of pizza

Subject Line 

Apart from the sender name, the subject line is a major deciding factor in whether your email gets opened. The Kulea blog is full of handy hints on getting your email content right and here are some of our top tips on subject lines: 

1 – Have one! An empty subject line is annoying, not mysterious.
2 – Keep it short. Your readers are just as likely, if not more likely, to be reading on mobile.
3 – Avoid SHOUTY CAPS.
4 – Don’t promise something you aren’t going to deliver.
5 – Be specific about how you are solving their problem.


There is a general consensus about text to image ratio of 60:40. More words, fewer images.

Include Alt text so that recipients who may, for whatever reason, have image loading turned off can get the jist if not the visual. 

There are guides on pixel sizes in Kulea’s nifty intuitive email designer. It means inboxes don’t get overwhelmed by images and emails look good across all devices.

There are also numerous studies that show that whilst people say they prefer image heavy HTML emails, they actually respond better to plain text emails by an average of 25% (source. Hubspot).

Effect of number of images in marketing email on CR

Call to Action

It is highly advisable to include a call to action in every email. How, otherwise, do you know if you have engagement with your audience beyond them opening the email?

Don’t go mad, though. Less is more in this case. 

Make them really clear by using coloured underlined hyperlinks and/or buttons and be specific.

Please don’t bury a clickable link in a picture unless the picture effectively says: “click this picture”.

Kulea is, as ever, here to help

You can’t go wrong with our intuitive design tools that you can use to easily place images, text, custom fields and more into your emails.

Kulea sends over 500,000 emails a month and keeps an eye on a LOT of customer emailing (not just yours), so we know what works. We are here for you.

We support you as you compose by signposting resources and best practice in content creation.


Check out the Useful Links section below

Tutorial: Use mail-tester to check your emails for spammyness

Check out these other articles on the Kulea blog

Useful Links

Here are the links from The Ultimate Guide that you might find useful

How reputable is your IP? – Senderscore

Is your tech set up OK? – MX Toolbox

How clean is your data? – Neverbounce

How spammy is your email? – Mail-Tester

Other useful:

What are Catch All email accounts? Neverbounce details on Catch-All email accounts

Kulea Blog Must Reads: 

The No Crap Guide to Cold Emailing

Creating a Content Marketing Campaign

Call to Action 10 Mistakes to Avoid 

How to Punch a Shark in the Face…

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