How To Improve Email Deliverability Rates


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In this post, we will explain what metrics needs to be monitored to optimise email delivery rates and how you can start to build the trust factors that will improve them.

What are Email Deliverability Rates?

Email deliverability rates determine the number of contacts that the campaign reaches as a percentage of the total number of intended recipients minus any contacts which hard or soft bounced.

For your campaigns to have their intended impact, they first need to be delivered to the recipient.

This is the first stage of email success that we outlined in our previous post The Importance of Email Preview Text In Mobile Devices.

Even if an email is delivered, it is unlikely to achieve its target if it is filtered into the ‘Spam’ folder by default.

Nobody enjoys receiving email spam and as a result, measures have been put in place to improve the quality of emails that we see in our inbox. This ensures that poor quality content is filtered out of the system before cluttering inboxes. Whilst these measures are great for email recipients, it is important the email marketers do not fall into the traps.

Email Campaign Reports

Make the most of your campaign reports

Email Analytics

To increase email marketing success, you need to look at your analytics. Analytics provide key insights into your recipient behaviours and trends in your email campaigns.

One key metric to analyse to gauge the deliverability of your campaigns is the percentage of email sends that are placed in the ‘Junk’ or ‘Spam’ folder. It is easy to see how many people have manually marked your email as spam, but keeping a close eye on your soft bounce rate will give you an indication of whether youa re triggering spam filters or not.

If you are, then you will see your soft bounce rate rise – sometimes dramatically- but this is not always the case. Benchmark your average soft bounce rate to monitor this going forward.

Emails which are identified by the Email Service Provider as acceptable to deliver but which are likely to be useless to the recipient will likely be placed in the ‘Spam’ folder by default.

A user may also choose to place the email in the ‘Spam’ folder after receiving it into their main inbox. In either case, the future deliverability of the sender’s email campaigns is negatively impacted, as you will no longer be able to send to this contact.

It is also important to monitor which part of the inbox your emails are placed into.  In inboxes such as Gmail, where there are a number of sub-folders within the inbox, you should collect data about which folder your email reaches.  When sending email marketing campaigns, senders should target the Primary folder to receive the most attention.

To achieve this, ensure that you test send your email campaigns to as many different email clients and devices as you can. This also enables you to check that the email is rendering correctly too.

My Email Delivery Rate is Poor, What Should I Do?

Whether the delivery rate for one of your campaigns is suffering or you have noticed a deterioration overall, you need to rectify the cause quickly.  Building trust in your email campaigns forms the basis for success.

High delivery rates often reflect good quality email campaigns with targeted high quality content, an engaged email list and good list hygiene practices.

Delivery Rates can deteriorate for a number of reasons and it can be hard to single out one individual cause.  To identify why your delivery rate is poor, you should look at your email analytics.  The good news is that you are in control of many of the reasons for poor deliverability and you can make changes to your campaigns and email habits to rectify the problem.

Sender Scores

A company’s sender score is calculated based on the sender’s IP reputation.  The sender score is used to compare the reputation of similar email accounts.  If your delivery rate is starting to decline, the sender score is a good starting point for examining the reasons why.

Return Path administer the sender scores. To find out what your sender score is you can visit their sender score page.

The score is calculated on a scale from 0 to 100.  Companies should aim to have a perfect sender score of 100, however one over 95 is considered good in most cases.  Achieving a perfect sender score is realistic where good practices are followed.  The more a sender score deteriorates the less likely it is that their email campaigns will be delivered.

Factors impacting the sender score include:

– The number of complaints
These are measured by the number of emails that you have sent that have been marked as spam manually.

– Volume of sends and regularity of sending
Consistency is key to a good sender score. If you are following best practice, such as segmenting your lists and sending relevant and timely communications, you should have a regular routine of sending and volume of emails being sent.

– External reputation
Do your email contacts trust you? If they are engaging and interacting then the ISPs will also trust you. That increases the sender score and increases delivery rates.

– Unknown Users and unknown user rates
How often do you send to email addresses that don’t exist? This is a big measure of how efficient your data collection is how effective your list hygiene processes are. Although it can happen, there isn’t much of an excuse for sending to email addresses that don’t exist.

– Accepted and rejected rates
How many of the emails that you send get into contacts inboxes? If a lot of them are soft bouncing, this is also a signal to the ISPs that all might not be above board. Do you need to change your copy so that it is less spammy? Are the emails that you are sending too large? Is there too much imagery in them and not enough text? THese can all affect whether you get put into a spam folder or not.

Companies should be wary of the number of complaints that they receive.  Although the volume of email sends does not directly impact sender score as a standalone factor, it is taken into consideration when calculating the percentage of emails which have triggered a complaint.

A sender who distributes two thousand emails in a campaign and receives two complaints will have a higher sender score than one which only sends two hundred and receives the same number of complaints.

However, the good news is that if you have a low sender score, the scores are calculated on a rolling 30-day basis so changes that you make will be quickly reflected.

Spam Filters


Spam Filters can cause your emails to be blocked before they reach the recipient’s main inbox. Spam filters are set up to identify when the the different aspects of an email contain spam triggers.

Adopting strong copywriting techniques is advisable to avoid triggering spam filters. There are many examples of copywriting techniques that cause emails to be automatically marked as spam.

Some examples of spam content that we have gathered are shown below:

Spam Triggers in Commerce Emails

As seen on Buy Buy direct
Buying judgments Clearance Order
Order status Orders shipped by shopper


Spam Triggers in Marketing Emails

Click here Increase traffic Notspam
This isn’t junk One time mailing Increase your sales
We hate spam Web traffic Will not believe your eyes


Spam email copy, when used excessively, indicates to the filter that the content of the email is low quality and probably irrelevant to the user. This copy also demonstrates that the email has been sent in bulk rather than with a particular type of recipient in mind.

Excessive use of capitalisation is also detected by spam filters; avoid writing clickbait email subject lines designed with the sole intention of attracting a recipient’s eye such as ‘You will not believe your eyes when you read OUR SPECIAL OFFER INSIDE!!!!’.

As you have probably guessed already, excessive use of exclamation marks or other punctuation should also be avoided. Writing your emails in clear, jargon-free language which is well punctuated is advisable.


When an email passes through the spam filter, any links contained within the email are also checked to ensure that they connect to legitimate websites and landing pages.

Link spam, where an excessively high number of links connecting to the same URL are contained within the email copy, is forbidden.

Some spam email senders hide links or malicious code behind other elements of the email such as images; as a result, such practices are monitored by spam filters.


The text to image ratio of an email is also checked at this point. Emails should contain a higher proportion of text than images (60% text and 40% image is around the lowest amount of text that you should include).

High image to text ratios are indicative of low quality spam content.

Alt-text should be added to any images that you choose to include in the email. In cases where the image cannot be displayed for any number of reasons, your alt-text will show in its place. The alt-text should be descriptive enough so that the recipient’s reading experience is not impacted in a text-only format.

Ensuring that your emails are not marked as spam is imperative for long term success.  Although your deliverability rates may remain high in some cases, if your emails have previously been identified as spam it is likely that your future sends are simply being filtered into the recipient’s spam folder.

Firewalls and IP Checks

Firewall and IP Checks take a detailed view of the deeper aspects of an email which is sent out by a user. The firewalls and IP checks look for spam accounts, account histories, the domain that the email originates from and whether the user has the necessary permissions to send an email from that IP.

All of this information is found in the “envelope” of the email:

Email Envelope

Screenshot of an email envelope

Firewalls exchange information between networks and computers to identify known spam accounts, sharing the knowledge that they accumulate over time. Known spam accounts can then be blacklisted by Internet Service Providers to ensure that none of their emails find their way into the email inbox.

When an email passes through a firewall, the existing users that the email address has sent to, is examined. A user who sends to a high volume of spam email accounts will likely fail a firewall check.

If a sender is responsible for sending a number of abusive emails to one particular recipient, they may choose to block that IP address to prevent any further correspondence.  Once an IP is blocked, it does not matter whether the sender sets up a new email account as none of the emails from that location will reach their intended recipient.

Email Size

Be conscious of the size of your emails. Some email sends may suffer low deliverability rates if your email contains large attachments or high-resolution images or GIFs. Bulky emails take longer to load when they are delivered but are also more likely to trigger spam filters.  Although visually appealing emails may be more attractive to the human reader, a balanced approach needs to be taken.

Remember: 60% as a minimum for text content, 40% as a maximum for images.

To provide your email recipients with a seamless experience, include a link to the page hosting the content you would have attached to the email. Another good alternative to large attachments is cloud storage. Cloud storage allows for the storage of files and document on a server. Provide the email recipient with the address of the file on the cloud and ensure that your file privacy settings allow the email recipient to use the file.

Steps to Improve Your Email Deliverability Rates

Avoid sudden changes to your email volume: 

If you want to significantly increase the number of emails that you send out on a regular basis, gradually increase emails over a period of time. Increasing your email volume suddenly and dramatically may slow down or even stop some of your emails from being delivered. Plan email volumes on a calendar to map out any changes, gradually increasing your email volume. You can also use that calendar to analyse when your deliverability suffers and whether the number of email sends was a factor.

Warm Up Your IP Address: 

When using a new email address, slowly introduce the email sends to your contacts. Ensure that the first few contacts that you send emails to are reliable, will not mark your content as spam nor unsubscribe from your communications. Sending a large email campaign from a cold IP address is likely to cause problems with your deliverability. Senders should take caution with their email activities until their reputation is established. Be alert and responsive to any patterns in your email analytics, if your emails are not delivered, take action before sending out larger campaigns.

Perform List Hygiene Checks:

Make sure that you are only sending to contacts who want to receive your emails. Sending your emails to a list of engaged followers who open and engage with your email content will improve your sender reputation. On the other hand, sending emails to disengaged contacts who ignore, delete, or worse, mark your emails as spam, will have a negative impact on your reputation. Removing known spam accounts, misspellings and deactivated accounts from your email list will reduce your hard bounce rate and increase your sender reputation.

Use Segmentation:

Segment your lists to ensure that you are only sending the most relevant content to your subscribers. This is a good way to avoid spam complaints if you are sending an email which is only relevant to a small number of your email subscribers. Reducing the number of spam complaints for your email improves your sender score and helps to build your reputation over time.

Email Segmentation

Download the Email Segmentation Whitepaper

Avoid Purchased Lists:

Collect contact details using methods which will ensure compliance with GDPR. Using purchased lists is not the way to collect data and will liekly result in a penalty when the new regulations are enforced in May 2018. Recipients on purchased lists (in most cases) have not opted-in to receiving your email campaigns and are more likely to disengage or report them as spam. Being marked as spam will impact the deliverability of future email sends.

Analyse Your Own Spam Folder:

Look at your spam folder for examples of emails which have been recently detected by spam filters. Spot any new patterns including any phrases that regularly appear in the subject line or body text of these emails and avoid using them in your own campaign.


Conducting an email test gives you a good opportunity to see which parts of your email are effective and where improvements can be made. Although tests are primarily useful to check your content, you can also ensure that your emails and any images they contain, render correctly in the recipient’s inbox.

Useful Resource:

If you liked this post, you will love “The Ultimate Email Subject Line Swipe File“!

To improve your email open rates, download it for free by clicking on the image below:

Ultimate Subject Line Swipe File

Download The Ultimate Subject Line Swipe File

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