Demystifying Deliverability 

Email Delivery


The Importance of Deliverability

Your email deliverability success is the most crucial aspect of your email strategy to take into consideration.

It’s all well and good spending hours on creative and segmenting your lists, but if your emails are not being delivered into your subscribers’ inboxes, then all your hard work has gone to waste.

There is often confusion around what the term deliverability even means. So we’ve put together this guide to demystify deliverability and equip you with the correct terminology as well as methods on how you can improve it.

So let’s start with a glossary of deliverability terms. There are two distinct areas to consider in this topic which are Delivery and Deliverability (or Inbox placement).

Delivery refers to if you subscriber’s inbox accepts your email or not. This step comes before the inbox or spam filter. The question to consider is can your email physically be accepted to their mail server in the first place?

Deliverability (or Inbox Placement) refers to where your email eventually ends up once it is accepted by the subscriber, be this their inbox, spam or another folder.

There are many factors that impact your email deliverability and we’ll outline a number of those throughout this guide.

What affects deliverability?

As you’ll discover there is no exact science to getting your emails delivered to your recipients’ inboxes, and there’s certainly no magic trick to getting it right.  But you can follow best practices for optimum results. The reasoning for this is that mail service providers (MSP) such as Gmail and Yahoo, are constantly evolving and developing new ways to protect their recipients from unsolicited spam. There are lots of different factors that ISPs (Internet Service Providers) look at, and to varying degrees, it depends on the particular ISP.

Your data and how you collect it
The most important way for ISPs to determine what happens to your email is to review your historical reputation from both IP/domain (your website address). Different variables have positive and negative repercussions. Such as moving emails from junk to inbox, deleting without reading clicking links, or marking it as SPAM. Therefore the best way to ensure an inbox placement is to make sure that all of your recipients want to receive your emails.

Ensure that when people sign up, you’re as transparent as possible and are setting expectations of contact. For example, tell people what you’re going to send them and how often, so that they aren’t surprised when they receive your emails.

Offer recipients preference options when they sign up. For example, they might not want to receive all of your emails, so have a preference centre in place that allows recipients to specify exactly what they want to receive from you. We will go into more detail about preference centres shortly.

You should be using a double opt-in email which asks recipients to verify their email address when they sign up. This ensures that the email addresses in your list are as legitimate as possible.

Make sure your privacy policy is publicised, not only is this a legal requirement, but this will help people feel secure when they sign up.

Your sender reputation
Once people are signing up to your email list, keeping them engaged is absolutely key. Have a look at the strategy section later on for further details.

Apart from subscriber engagement levels, other important factors to consider that affect your reputation include:

Complaints – Even a tiny number of recipients marking your sends as junk can severely impact on your overall deliverability.
Bounces – ISPs will also look very carefully at your soft and hard bounce rates. If you send to addresses which are no longer valid this will generate a bounce. These are seen as a sign of poor list hygiene and could result in your sends getting junked.
Spam Traps – These are usually old email addresses that are left active as ‘traps’ for marketers with bad data sourcing methods. Once emails are received, the sender is identified as one with bad data collection methods and is usually blocked by some or all of the major ISPs.
Sending Volumes and Consistency – ISPs prefer that you have a consistent pattern of sending. If you suddenly increase your sending overnight by a large percentage or have a large spike in volumes after not sending for a week or two, inboxes are likely to become wary of your sends which results in soft bounces i.e. that campaign won’t get through but your next one might. We explain more about hard and soft bounces later on.
Blacklists – These are lists of either IP addresses or sending domains that have been previously identified as dangerous senders, usually through hitting spam traps or having high numbers of complaints.

Your content
Different ISPs look at the types of content that you’re sending in a variety of ways. Typically there are some key areas to watch out for:

Don’t link to websites that have been reported as sending spam in the past. Use a site such as to check this.
Ensure you’re not using link shorteners, as it will look like you’re trying to hide malicious url’s.
Don’t send attachments, as these get flagged as dangerous, so link to them instead.
Some inboxes prefer you to have a 60/40 split of text to images. This doesn’t have to be exact; just make sure that you include some images and that they’re not touching each other in your html.

Lastly, ensure your unsubscribe link is clear and visible. There’s no point trying to stop people from unsubscribing, as all they’ll do is mark your sends as spam.

Email Deliverability

Strategies for keeping your deliverability healthy

ISPs such as Gmail and Outlook have various rules in place to encourage senders to follow best practice in their email marketing. What this means is that as long as you’re sending people the content that they’ve signed up to receive at the frequency they’ve requested, ISPs should recognise this in your results and your deliverability will improve as a result.

Maintain a healthy contact list
One of the biggest downfalls in terms of deliverability is to keep sending to people that are no longer engaging with your emails. Your email service provider (ESP) will start to recognise this, and by using machine learning will begin to assume that people don’t want to hear from you any more, sending your emails to junk as a result.

You can combat this by looking at the last open date of each of your contacts, and build a contact and re-engagement strategy around this.

If people haven’t opened an email for three months, set up an automation message with a different style of subject line that attempts to get them engaged in your sends again.

If people still haven’t opened for six months, then create a different contact strategy for them. A nice simple way is to create one segment for all your ‘engaged’ recipients and one for your ‘disengaged’. Send a few carefully chosen sections of content to all of your engaged subscribers once a week, and then at the end of the month chose the best performing ones from those sends and send these to the unengaged segment. That way the people that are engaged get lots of good relevant up to date information, but the ones that aren’t just get an occasional reminder that you’re still there with the very best performing content.

Be warned that old addresses will sometimes get recycled into spam traps, so all the old addresses that you keep emailing could end up doing serious damage to your deliverability.

Sending to unengaged contacts from the same domain alongside sending to highly engaged records can result in your engaged subscriber emails suffering from a reduced level of overall deliverability.

Also make sure your unsubscribe link is very clear on any sends you’re sending to unengaged data. If recipients can’t find it after a few moments, they’ll likely mark your email as spam and your deliverability will suffer as a result.

Set expectations of contact
As previously mentioned make sure you’re telling people at the point of signup what they’re going to be receiving and how often. This is the perfect way to ensure from the start of your relationship that they know what to expect from you. If you’re only going to send one newsletter a month, tell people so they’re expecting to hear from you. If you’re going to be sending the latest deals and offers from your website, tell them- then they won’t get any surprises and be tempted to mark you as spam.

Send a welcome email
Welcome Emails also serve as a great opportunity to set expectations of contact, they can also be a great opportunity to start your relationship with your new subscribers on the best possible terms. Reinforce and remind people of all the great reasons why they signed up in the first place, tell them when to expect emails from you, or even tell them about your social channels so they can keep up to date with what’s going on between your email campaigns and get them even more engaged with your brand.

Use a preference centre
The key with successful email marketing is giving people the type of content they want to receive to ensure they stay engaged, so let them tell you- set up a preference centre with options for the type of updates they receive so it’s completely in your recipient’s hands.

Ensure recipients receive emails from the brand they signed up with
If they added their email address to and they start receiving emails from, then they’re more likely to mark the email as spam, so be sure to send your emails from a domain they will recognise.

If you are sending on behalf of someone else, make sure it’s very clear on the signup form that this is what’s going to happen (setting expectations of contact), and on the email make sure you tell people “you signed up on but we said we’d send you a few related offers that we’ve carefully chosen. Please unsubscribe if you’ve changed your mind”.

Are you sending the same message out to all of your email contacts or have you tried segmenting your list? If you’ve been collecting lots of data about your recipients then this will be easy enough to do.

Segmenting your lists will ensure your subscribers receive content that is only relevant to them, ensuring higher open rates and engagement and minimising the chance of unsubscribes.

Making messages feel more personal and more targeted can increase engagement dramatically. If you’re new to personalisation, consider starting simple by just adding your recipient’s first name into your campaigns. A small touch like this can make a message feel much more targeted.

Content and Design
If your engagement levels are low consider reviewing the design of your emails. Having an attractive looking email, which follows email best practice can go a long way.

A few things to watch out for:

  • Do you have clear visible calls to action?
  • Is your image to text ratio good (Best practice is 60:40)?
  • Strong consistent branding across the message?
  • Good size, quality and positioning of images?
  • Is there a good contrast between text and background colour?

Subject lines
Your subject line and pre-header text are your first chance to grab a subscriber’s attention. Your subject lines should be attractive enough to make the person open your message.

Try personalising your subject lines. Personalisation in subject lines works the same as it does in the body of the email.

Consider doing some subject line testing, this can help you identify what kind of subject lines are attractive to your subscribers.

Sending at the optimum times?
There is a lot of information out there on when the best time to send a campaign is. This varies across industry and the best way to find out is to look at your own engagement levels at different times and find the best time for your own recipients.

You can get help from ESP tools such as Pure360’s Intelligent Time Sending, which will send your campaign out over a 24h period, finding the optimum time to send to each recipient based on their previous behaviour.

Are you sending a resend to non-opens?
Doing a resend of your email can be a second chance for your email to get opened. Setting up a resend with our built in feature couldn’t be easier. We’d recommend to send exactly the same message, just with a different subject line. You can adjust the subject line slightly or change it completely – it’s entirely up to you.

Pre-send checklist
Make sure to use our pre-send checklist for your campaigns.

Email Deliverability

Avoiding SPAM filters

Like all your email content, subject lines are subject to SPAM filters. A subject line containing a SPAM trigger word may skip the inbox and end up in the SPAM box. The same goes for special characters or sudden capitalisation of words.

Common SPAM trigger words and phrases include:

Call free
Call now!
Free offer
Free quote
Money back
No fees
Risk free
Offer expires

A strong sender reputation could allow you to use these phrases and not be detected as SPAM, but even if you get past SPAM filters, these phrases may be red flags for the recipient due to their association with spammy and deceptive emails.

What else can you do if you have a deliverability issue?

If your emails are being sent to your recipients’ junk folder, or not being delivered at all, there’s plenty you can do to determine why this could be happening:

Test your email to a different inbox. Even if Gmail isn’t accepting your emails, Outlook may still be, so it’s helpful to know how widespread the issue is.

Try changing the subject line of your email to something completely different to see if this changes your results.

Swap the subject line of your email out with some safe plain text. You can generate some of this to use on sites like If this results in your email being delivered, it suggests there is a problem with your html. If your email is still having problems, it could mean there is a problem with your sender reputation.

Try comparing your campaign to a previous one that you know didn’t have any issues, and swapping in some of your new content with the old content to see if this affects results.

Use a domain checker such as to ensure your sending domain doesn’t appear on any blacklists.

Make sure that your hard and soft bounce levels haven’t increased recently. If they have it’s possible that ISPs are viewing your sends as potentially dangerous.

If your sending volumes have increased recently it is possible that ISPs are rejecting some of the extra volume while they determine if your emails are safe, if the difference is large enough all of the volume will be affected,  however it would have to be a large jump for a dedicated IP/domain to be affected.

Points to Consider

– If you are sending HTML content, ensure you also have a plain text version
– Don’t make your subject line all capitals
– Make sure your ‘from name’ (sometimes called ‘friendly from’) is an actual word(s) and not a URL – i.e.: don’t put .com at the end of it
– Ensure your HMTL content has at least 3 images and not all of them touching
– Ensure your HTML content has at least 60% text and at most 40% images


Email Deliverability

Glossary of Deliverability Terms

– Blacklist – These are lists that ISPs use to mark you as a sender of unsolicited email. Getting on one of these lists can make it very difficult to get your emails delivered, and getting removed from them can be very tricky.

– Block – When mailbox providers such as Gmail or Outlook reject mail from a sender and don’t deliver mail to recipients, often based on the reputation of the sender.

– Dedicated IP address – a single IP address that mail is sent from. This allows the sender to be in complete control of their sender reputation as ISPs can easily identify them and reward them for following best practice guidelines.

– DKIM –  DomainKeys Identified Mail is a common method and soon to become a global standard of sender verification that many ISPs use to determine reputable senders.

– DMARC – Domain-based Message Authentication, Reporting & Conformance is another common method of email authentication that ensures senders are correctly following DKIM and SPF standards.

– Domain – A senders registered online, eg

– Double opt-in – A double opt-in email is automatically sent when a recipient signs up to your emails. It provides a link for the recipient to click to confirm their address and complete the sign up process. This ensures that sign ups are using authentic email addresses, as well as confirming they have been entered correctly.

– Email Service Provider – a company such as Pure360 who provide email services, including batch email and email marketing.

– Hard bounce – This refers to when your ESP tries to deliver an email to an address, but the receiving mail server tells us that the email address can’t be delivered to. It may have been closed down for instance.

– IP Address– A unique address that identifies a device on the Internet or a local network. It allows a system to be recognised by other systems connected via the Internet. In email marketing, your IP address identifies you as a sender, and also carries a reputation that helps ISPs determine whether they should deliver your emails or not.

– ISP – Internet Service Provider, in this case we’re referring to mailboxes, so Gmail,, Yahoo, btinternet and AOL are the major ISPs that you’ll interact with.

– Open rate – This refers to the percentage of recipients that have opened your emails, taken from the total number you originally sent.

– Sender Score – Sender Score is a free tool created by Return Path which allows you to monitor the reputation of your IP address. It’s a useful guide to determine any issues.

– Soft bounce – When your ESP tries to deliver an email to an address, but the receiving mail server tells us that the email address can’t be delivered to on this occasion, but is still valid. A full inbox is a good example of this.

– Spam feedback loop – Some mailboxes such as Yahoo and allow email senders such as Pure360 to subscribe to feedback loops. When someone clicks on the ‘Spam’ button, they send a message to your ESP and they make sure they opt that recipient out of any future sends.

– Spam trap – These are typically old email addresses that have been turned into ‘traps’. They are monitored by ISPs and blacklists to see if they receive emails and when they do, the sender is usually blocked or put onto a blacklist.

– SPF – Sender Policy Framework (SPF) is a simple email-validation system designed to detect email spoofing by providing a mechanism to allow receiving mail exchanges to check that incoming mail from a domain comes from a host authorised by that domain’s administrators.

– Spoofing – This is when the sender address and email header are changed to look as though the email originated from a different source. This is generally considered to be bad practice.

– Temporary email addresses – These are non-permanent email addresses that people can sign up to for a short period of time, usually to avoid using their own email address. If you’re seeing a lot of these in your data, it usually means that people don’t trust you enough to submit their real email address.


As you can see that there are a wide range of factors that will affect your email deliverability.

We advise that you regularly check the key areas that we have outlined in this guide to ensure maximum deliverability. Create your own checklist and build your emails based on best practice. Personalisation and segmentation is key to ensure your subscribers are receiving the content that is relevant to them and reduce the risk of unsubscribes.

We offer a full review of your deliverability as part of our managed service packages, so please feel free to reach out to us and we’ll be happy to help.

Email Deliverability

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