Getting your emails delivered can be frustrating. Many find that when they begin a mailing list, few of their customers notice at all because they are unable to get their mailing list emails to land into their customers' inbox. Rather, they reach out to their customers and find that their emails are being automatically sorted into the spam or junk mail folders.

Some may be quick to assume that their domain has a bad reputation, that the content of their emails is somehow precarious or even that their customers are reporting their emails and causing them to be flagged. In our experience, poor email delivery is nearly never due to the reputation of the sender; more often than not, we find the root cause to be simple configuration issue(s).

This article discusses common configuration problems that may be causing your newsletter or marketing emails to be undelivered or land in your customers' junk or spam folders.

Reason 1: You are sending emails from your corporate email domain without sanctioning the mail delivery server

The most common email configuration error that we observe is also the most simple error to correct. It occurs when you send emails on behalf of your corporate network (for example,, but you do not update the public list of mail servers that are allowed to do so. This is called an SPF record.

If your organization currently uses Office365 or Google Workspace for emails, then your domain has probably been configured in the past with one of the recommended starter SPF records from that provider. These are only a very basic configuration and they usually need to be customised to include any of the other services you use. For example, if you use a bulk mailer such as Mailchimp, then they must include the Mailchimp servers.

You can find out easily if your corporate network is configured with an SPF record. Suppose that your sender looks like, then your corporate domain would be You can use the SPF check and SPF lookup tool to find your existing SPF records. This will tell you whether an SPF record was found, and what that record may look like. Our record looks like this:

v=spf1 -all

If you use a bulk mailer, you should see it in this list. If you do not, you are not alone; many businesses publish incorrect SPF records. But you should correct it if you do not want your emails to be sorted into the junk or spam folders.

Reason 2: You are sending digitally signed emails from your corporate email domain, but your mail delivery service is not signing emails or using the wrong signatures

Perhaps your corporate emails are digitally signed to prove that the emails originated from someone within your organization. The mechanism for email signing is called DKIM, and email signing is a very common and recommended email configuration, especially for Office365 and Google Workspace customers.

The configuration of DKIM involves publishing a pointer to a cryptographic keypair at your domain. Each mail service would usually have their own keypairs that they rotate from time to time. If this configuration has been completed correctly, mail that you send would be compared against the certificates that you have published, and if they do not match then it would indicate that the mail was probably send fraudulently.

The problem often occurs that, when we are using a bulk mailing service like Mailchimp, we can forget to publish pointers to the keypairs that our bulk-mailers are using, and so the mail that reaches our customers does not pass the signature check. In this case, it appears as though it had originated from an impersonator and it is common for it to be silently discarded into the junk or spam email folders.

Reason 3: You are sending emails from an address that your customers do not typically interact with

Perhaps you normally interact with your customers from your personal corporate email, and in many cases they probably respond to your personalised and direct emails. But suppose that you were to subscribe them to your mailing list, and you notice that they are not engaging with your newsletters. Perhaps they have not even opened them. What is the difference, and why is this the case?

Deliverability can vary greatly depending on whether a user has interacted with a person before. This difference can be illustrated like this: if a customer reaches out to your business to make contact, their email client knows that they are interested in hearing from you because they had initiated first contact. But more often than not, if it is the other way around and you try to make contact with a potential customer from an email address unknown to them, it can easily land in the junk, spam or promotional areas of their email client because they were not expecting to hear from you.

This is also the case when thinking about how your mailing list emails are delivered. If you send them from an email address that doesn't represent someone at your company that they have interacted with before, then they will be delivered less successfully than if you address them personally from somebody that the customer interacts with regularly. There is only one caveat to watch out for; as usual, make sure that your email communications are solicited, as it will be more detrimental to you if your personal corporate email is repeatedly reported or marked as spam.

Reason 4: You are sending emails that are too complex or use features that are not understood by email clients

We all want to make a good impression to our customers, so we may spend a lot of time styling our mailing list emails so that they look appealing. Most of the emails that we send will be based on HTML. We need to be careful though, because not all of the features supported by HTML are actually understood by email infrastructure. It is important to limit the features that you use in your emails, because when you use features that are not properly understood by email servers or clients, this can lead to your emails failing to render or only rendering partially.

Even if your customers' email readers can understand the emails that you send, using emails with a complex structure may still cause upstream filters or servers to be unable to correctly parse their content. If the content of the email is not simply understood, this can lead to them erroneously detecting a lack of meaningful content for the reader, and the email may be sorted to the junk or spam folders instead of the inbox.

With this in mind, you should limit the features that you use in your emails to the features that are supported by the most basic email infrastructure:

  • Use static, table-based layouts with simple nested tables
  • When styling elements, always use inline CSS and avoid using classes, identifiers or style tags
  • Do not use features such as background images, image maps, stylesheets, javascript, frames, flash, embedded audio or video, forms or HTML5 semantic elements

Once you have composed your email, you should ensure that there are no errors, such as open tags, in the markup. You can use the validator tool to check this. To pass validation, aside from fixing all semantic problems with your emails' source code, you will need to ensure that it has all of the necessary metadata in its structure. To learn more about the technical details of structuring email, you can read this article.

Reason 5: You are sending emails that do not contain unique content or content that identifies the recipient

The last point that we shall consider is to ensure that the emails that you are sending contain all of the information that email infrastructure expects to see from high quality corporate marketing content. Our email clients know that users rarely interact with low quality marketing emails, so they will often hide this content from us. You should ensure that the body of your email contains the following essential pieces of information mandated by the CAN-SPAM Act:

  • The email should contain as much personal information about you as you can provide, such as your full name, your position, the organisation that you represent, the website of your organisation, your phone number and your full mailing address including the country and postcode
  • The email should make it easy to unsubscribe and should feature an inline link with the text "Unsubscribe"

You should also ensure that each email that you send has a unique subject line, where the main theme of the communication is apparent in the first few words of the subject line. You may also include this subject in the <title> block.

When writing your email, make sure to include an accurate and informative pre-header so that when your email is parsed, the unique content can be detected in the first few lines of your email. Each email should look unique in the reading pane.

You may know the first name of the person that you are sending the email to. If you do, you should always mention their first name in the first few sentences of your email. You can also mention it in the pre-header. This personalises the email, giving the content of each email a unique hash (making it more difficult to detect duplicates), and also proves to the users' email client that the user was probably expecting to receive your email.

You should limit image content in your emails. If your email includes any image content, ensure that image content is not necessary to read or gather the main points of your email. Most email clients and email infrastructure do not even download, let alone parse images unless the sender has added you to their list of trusted senders. So if you include your contact information, title blocks or other important information as part of an image (for example, it is common but a bad practice for people to use a precomposed image signature), this can lead to it being separated from the main content of your email. Assume that image content will not be displayed, and if your email relies heavily on image content than it might find itself in the junk or spam folders.

Finally, you should always test your emails across multiple email clients before sending them. There is a lot of inconsistency across various email clients. Remember, not everyone uses the same email client that you do; different email clients have different reading pane widths and support different HTML and CSS features. Different clients can also have different base styling, which can cause content to become invisible. Emails that display on web based clients may not display any content at all on desktop or mobile clients, or vice-versa. If some of your content is obscured from the reader, this can raise a significant red flag. Litmus is a great option for testing across a vast variety of different email clients.


It is difficult to guarantee that emails are delivered. Sometimes, even if you do everything correctly, after a few years your mailing list emails may begin to land back in the junk or spam folders. It is a continuous scientific process to stay ahead of the algorithm. A well-known pioneer of modern computing once said:

“Theory and practice sometimes clash. And when that happens, theory loses. Every single time.” — Linus Torvalds

If you find that the points above may apply to you, or you think they may, but don't know how to check, you can reach out to our team and one of our friendly and highly-skilled engineers can help you. If you have a long-running email campaign and this has only recently become a problem, perhaps you need some fresh ideas. Either way, we're happy to help. The first step is to reach out.

Let us know in the comments what techniques have helped you to improve the deliverability of your email campaigns.

5 Reasons Why Your Mail Might Not Be Getting Delivered