Guide to Improving Email Delivery


When you send your marketing emails, you’d like to believe that every mail reaches the intended recipient. Achieving and maintaining a high delivery rate is a team effort, and Everlytic works hand-in-hand with you to achieve the best results possible.

Each email goes through a series of checks between when you send it and when it is delivered to your subscribers (or not), and there are a number of actions that you can take before sending the email which will help improve your chances of a successful email campaign.

In this guide we will cover everything from collecting names to maintaining a clean mailing list, and how you can layout and write your email for the best chance of success. We will also cover technical issues behind how emails are marked by Everlytic, as well as how email clients (e.g. Gmail and Yahoo) check to make sure that your email has come from a legitimate sender (you) and is not spam.

Journey of an Email

Email doesn’t travel straight from your server to your recipient, it goes through a number of checks and filters in between.

When you send an email with Everlytic, and most other service providers, your recipients list is first scanned to make sure you don’t send to any suppressed email addresses. This will ensure that your email isn’t sent to people who have unsubscribed from your list.

When a subscriber unsubscribes from your mailing list with Everlytic, we don’t delete them from the list, we mark them as ‘Off’ so that their preference is recorded.

If your Email Service Provider(ESP) is accredited with a service, such as Return Path, your email will be delivered to your recipient’s inbox.

If your EPS is not accredited, your email will undergo the following checks:

  • Authentication: SPF, Sender ID, and Domain Keys are checked.
  • Reputation: Blacklist, volume, bounce management, and behaviour checks.
  • Content Filtering: Images, copy, subject, and links are checked.

If your email passes these checks, it will be sent to your subscriber’s inbox. If it is suspicious, but not obviously spam, it might be filtered to the Junk or trash boxes. If the recipient’s email service provider decides that your email is too much like spam, you could find it is hard-bounced and denied completely.

Technical Requirements

This one is on us. There are a number of technical requirements for every email sender which we can use to tell email servers that Everlytic, and our clients, are legitimate email senders.

Email Spoofing

Email spoofing is a specific type of spam which involves creating email messages with a forged sender address. You probably know it as “phishing”. You may have encountered this with an email that looked like it came from your bank, but it actually came from a spammer who was hoping to trick you into giving them your online banking login details.

That’s email spoofing.

Technical Info

When an email is sent, the initial connection provides two pieces of address information (sometimes called the envelope):

  • MAIL FROM: Normally presented to the receiving server as the Return-path: header, but not normally visible to the end user. Generally speaking, no checks are done that the sending system is authorised to send on behalf of the email address.
  • RCPT TO: This specifies which address the email is sent to.

If the receiving email server accepts the envelope, the sending server will send the email header.

  • From: Joe Blogs <>: The email address visible to the recipient. No checks are done that the sending server is authorised to send on behalf of this address.
  • Reply-to: Peter Pan <>: Similarly not checked.

The Sending server may also provide:

  • Sender: Jin Jo <>: Also not checked.


Spoofing is generally difficult to detect as the email recipient, but there are a number of effective counter-measures which are quite effective against spoofing. These counter-measures are all instituted by Everlytic, and other email service providers.

Sender Policy Framework

Sender Policy Framework (SPF) is an email validation system which allows receiving email servers to check that incoming mail from a domain is authorised by the sending domain’s administrators.

In order to comply with SPF, Everlytic must complete the following three tasks for every domain on our servers:

  1. Publish an SPF Policy: This policy must identify the machines authorised to send email on behalf of the domain/host, using the machine’s IP address.
  2. Check and use SPF information: Receiving servers use DNS queries to discover the IP address of the sending machine. The receiving server must interpret that IP information and act upon the result.
  3. Revise mail forwarding: Simply forwarding email is not allowed under SPF. The alternatives are:
    • Remailing
    • Refusing
    • Whitelisting
    • Sender Rewriting Scheme

DomainKeys Identified Mail

DomainKeys Identified Mail (DKIM) is another method of detecting spoofed emails. DKIM allows receiving email servers to check that an email was authorised by the owner of the domain it claims to have come from.

DKIM lets a domain digitally sign an email using the signer’s public key published in the DNS. This signature is attached and verified by the email servers, and is usually not visible to the subscribers themselves. DKIM signatures, when valid, guarantee that an email hasn’t been changed since the signature was attached.

If the signature fails to verify, the message won’t necessarily be automatically rejected. Instead, the reasons for the verification failure should be provided to the sending and receiving servers, either via a feedback loop or by adding a header to the message.

Using DKIM

Using DKIM makes it easier for signing domains to identify legitimate email senders. This makes blacklists and whitelists more reliable.

  • DKIM itself doesn’t filter or identify spam, but using DKIM prevents spammers from forging the source domain and address of their messages. Reliable sending domains can build up a good reputation and receiving servers can maintain whitelists of trustworthy domains.
  • If a domain is heavily phished, legitimate senders in that domain can use DKIM to sign and verify their emails on sending. That way, if an email originates from that domain without the DKIM verification, receiving servers can subject it to more security checks.
  • DKIM is backwards-compatible with email systems that do not have specific DKIM support. This is because it is implemented using DNS.
  • Each email needs to be individually signed when using DKIM, as a result this creates computational overhead (computational resources such as time, memory, and bandwidth) not required for sending without DKIM.
  • DKIM's non-repudiation feature prevents senders from credibly denying having sent an email.

Domain-Based Message Authentication, Reporting, and Conformance

Domain-based Message Authentication, Reporting and Conformance (DMARC) is built on top of SPF and DKIM and allows the administrator of a domain to publish a policy on which protocol (DKIM, SPF, or both) is used when sending email from that domain, and how receivers should deal with failures. Importantly, DMARC also gives powerful reporting capability to domain administrators, so they can improve protection from spam mail.

DMARC works by checking if the domain in an email’s From field matches the authenticated sender domain names. If either the DKIM or SPF checks pass, the DMARC alignment test will pass.


Once a day, the DMARC submitter will issue an aggregate report which it will send to the email sender. This report shows whether or not sending email domains passed or failed SPF and DKIM tests during the reporting period.

The DMARC reports allow legitimate email senders to find problems in their domain setup (such as From domains not aligning with the DKIM signature), rectify them, and pass future DMARC tests.

Avoiding the Spam Trap

The protocols we have discussed so far, SPF, DKIM, and DMARC, are important because they allow Everlytic to establish ourselves as legitimate bulk mail senders. Once we have a solid reputation for sending email that people want to receive, email service providers are more likely to add our IP addresses to their trusted list.

All of this helps you to get your email into your subscriber’s inboxes.

Now that we’ve looked at what Everlytic does, let’s have a look at what you can do to improve delivery rates.

Subscriber List Hygiene

Good email list hygiene is essential. List hygiene is the practice of keeping your email lists clean and making sure subscribers are active. By removing invalid and duplicate email addresses, and setting unresponsive contacts so they no longer receive emails, you will improve your chances of successfully reaching the inbox. We recommend that you clean your data on a quarterly basis. Data errors can creep into your mailing lists at any stage during a list-building campaign.

Some factors that cause dirty data are:

  • Duplicate records,
  • Stale or incomplete data, and
  • Improper data collection methods.

Email service providers calculate how many of your subscribers open and click links within your emails, unsubscribe, or are inactive. Constantly sending to contacts who don't want to receive your email, or to stale inboxes, can result in your sender reputation decreasing to the point where your emails are automatically marked as junk. In the worst case, you may even be blacklisted by the email service providers.

A thorough, consistent list hygiene practice will find the following in your lists:

  • Sender reputation threats (e.g. spam traps, honey pots, etc.)
  • Inbox delivery threats (e.g. bots, spammers, spelling errors, etc.)
  • Customer conversion threats (e.g. false usernames, profanity, etc.)

List Hygiene Tasks That Everlytic Does For You

We understand how important good list hygiene is, and Everlytic has a variety of built-in tools which automatically take care of some list hygiene tasks for you.

  • Everlytic doesn't import duplicate contacts.
  • The system deactivates unsubscribed and permanently bounced email addresses.
  • The optional SMS on bounce feature sends notification SMSes to bounced contacts (if their mobile number is in the system) to ask for a new email address. If the contact replies, the system automatically updates their records with the new address.
  • Everlytic doesn't import role-based accounts.
  • Everlytic doesn't import incorrectly formatted email addresses. When importing contacts Everlytic automatically checks that the email addresses are in a valid email format, e.g. or Anything other than the accepted format is not imported. This is one way of rooting out invalid email addresses.

Proper list hygiene can be time consuming if your list is in a bad state, but it is absolutely worth it in the long run. Clean email lists perform better, giving you higher open and read rates, and a better ROI than lists where you're sending to many uninterested, or non-existent contacts.


Your email properties tell subscribers and receiving servers who the email is coming from and what the message’s content is about. You might not think that there’s much you can do to improve deliverability here, but you’d be surprised at how a few simple steps now could impact delivery down the line.

SubjectThe subject line your subscribers will see when the mail arrives in their inbox.
DescriptionIf you want to add a description for your email, you can enter it here.
From NameThe company name that you'd like your subscribers to see when they receive your message in their inbox.
From EmailThis is what your subscribers will see as the 'From' email address in their inbox.
Reply-to EmailThis is the email address that subscriber’s reply emails are sent to.

It is very important that you use proper, monitored email address as your From and Reply-to email addresses. When subscribers reply to your emails, you need to respond to them. Email service providers track communications between subscribers and email senders, and if they discover that you aren’t engaging with your subscribers you will be penalised.

Email Composition

Another vital part of improving email delivery is the content of the email itself. You can avoid triggering spam filters by making sure your emails don’t look like junk email.

  • Steer clear of spam trigger words in your subject lines. Obvious culprits, such as ‘Viagra’, will guarantee your email lands in Trash, but phrases such as “be your own boss” and “Free offer” could also see your deliverability suffer.
  • Design your email to incorporate attractive media, such as images and small gifs, but not be dominated by them. An email should be mostly text, and email service providers will block messages with an image-to-text ratio that is too high.
  • Send consistently. Choose a sending schedule and stick to it. Once a week works well if you are generating a lot of new content, once every second week is better if you have less new content to share. If you send inconsistently you risk your subscribers forgetting who you are and why they signed up to your mailing list, which could potentially result in them marking you as a spammer.

  Also, make sure your emails are consistently branded with your corporate identity so that recipients can easily identify you as the source.

  • When personalising your emails, make sure you use your recipient’s correct name.


Testing is a very important facet of improving deliverability. With Everlytic’s testing tools you can ensure your emails meet all the spam requirements before you send them. More than that, you can experiment with subject lines and content layout to see what your subscribers respond to better.

Spam Test

Everlytic has a built-in spam test. When you run the spam test, the system will automatically evaluate the different elements in your email that contribute to a high spam score. The lower your spam score, the better.

AB Testing

Everlytic’s A/B Split Testing tool is a powerful way for you to try different email design and content strategies. The tool allows you to send two versions of the same email to two groups of contacts. Everlytic then tracks all the contact engagement statistics, and shows you which of the two emails elicited the best response from your subscribers.

There are many different email components you could test with A/B split testing, but for improving deliverability, you should focus on:

The most important part of an A/B test is that it has a defined, measurable outcome. You need to know exactly what you are testing. Here are a few ideas for things you can test:

  • Email subject
    • Personalisation vs. no personalisation
    • Shorter vs. longer subject lines
    • Brand name in subject line
  • Graphics
    • Larger vs. smaller graphics
    • Photographs vs. animations

Monitor your A/B reports carefully to see which changes improve your delivery rates.

While content changes might not have a direct impact on deliverability, they do help you build up trust with your recipients. If your recipients trust you, they’ll open emails from you. That will increase your reputation as an email sender, and the service providers will recognise that, and reward you for it by letting more of your emails through.


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