successfully delivered emails

Ensuring High Email Deliverability or How To Reach Your Subscribers’ Inboxes Successfully

Email marketing remains a tried-and-true marketing channel that businesses of all sizes can leverage to forge meaningful connections and foster engagement with their audiences. However, the success of any email campaign is determined by one critical factor: email deliverability. And even though clicking the “Send” button seems straightforward, the journey an email takes to the subscribers’ inboxes is fraught with challenges, and as a dedicated sender, you aim to navigate that road with care. 

That is where we come to the rescue by helping you understand how email deliverability works, breaking it down into main components, outlining the role and actions taken by the email service providers and your tasks as a sender, and eventually giving you the right formula for hitting those subscribers’ inboxes successfully.

Understanding Email Deliverability

Email deliverability refers to the ability of your emails to reach your subscribers’ inboxes, not their spam folders. It plays a pivotal role in the success of any email campaign and encompasses both technical and strategic processes that ensure your emails land in your subscribers’ inboxes. This capability is the cornerstone of what email marketing is, serving as the critical first step in a sequence that leads to customer engagement and, ultimately, drives conversions and sales.

Why Is Email Deliverability Important? 

In the digital marketing world, the journey of an email from sender to recipient hides many obstacles, including server responsiveness, changing algorithms of email service providers, stringent spam filters, and the constant battle to maintain a good sender reputation. These challenges make email deliverability a significant factor you should consider in your marketing strategy.

Imagine the scenario where you’ve dedicated considerable time to design an email campaign: you’ve polished the subject line, tailored the message to resonate with your audience, segmented your audience for maximum relevance, and added a good CTA. However, these efforts depend on one critical factor – whether your email is successfully delivered to your audience. An email that fails to reach the subscribers’ inboxes is equal to a billboard placed in a desert – it may be a masterpiece, but if no one sees it, the opportunities for engagement and interaction are lost.

An undelivered email, whether lost in the spam folder or bounced back completely, wastes your campaign’s potential and reflects negatively on your sender reputation, affecting future delivery efforts. Therefore, a combination of robust and trustworthy email infrastructure and compliance with email marketing best practices are essential to ensure your messages reach your clients and prospects. 

Factors Influencing Your Email Deliverability Success

Several major factors influence your email deliverability rate, each playing a crucial role in the overall success of reaching your subscribers’ inboxes. 

  • Email Infrastructure 
  • Sender Reputation (and sender score)
  • Domain reputation
  • Quality of the email list (bounces, SPAM, compliance)
  • Email Content

Now let’s deep dive and break them down!

Email Server infrastructure

The journey of an email from sender to recipient is full of potential obstacles, starting with the very existential risk of a mail server failure and your emails not being sent (on time) due to your sending server being unavailable. To prevent and minimize the risk of such a fundamental problem, it is recommended that you work with experienced and trustworthy email service providers that manage many clients and millions of emails daily and are able to provide infrastructure redundancy and quick problem resolution. 

For us at SiteGround, we not only offer email marketing services but also email hosting services. Over the past 20 years, we have built unmatched expertise managing email servers on both sides of the barricade – the sender side (what all email marketing platforms do) and the recipient side (what normally hosting companies and email service providers do). We manage the sending of 6+ million emails on a daily basis on average and also receive a similar number of millions of emails as well. This huge pile of knowledge that we have accumulated has resulted in multiple infrastructure and server-side customizations, as well as software solutions that increase the deliverability of the emails sent from our platform and reduce both outgoing and incoming SPAM. All that has made us one of the leaders when it comes to email deliverability

Unmatched Infrastructure Redundancy

Our highly redundant email infrastructure is designed to provide continuity and utmost resilience for all our email marketing services. We maintain multiple alternative, fully functional email infrastructures and our software that manages the email sending is able to switch between them in minutes. This means that if one system encounters any form of technical difficulty, another one is ready to take over the task of sending your emails without any delay or disruption. These infrastructures are hosted in different data centers, eliminating the internet connectivity factor and all sorts of major data center failures like power outages, natural disasters, etc.

Imagine it as having two skilled pilots in the cockpit of an airplane; if one is unable to fly, the other is immediately ready to take control, ensuring a safe and uninterrupted journey for all on board. Similarly, our multi-infrastructure approach ensures that your email campaigns are always on course, reaching your audience as planned.

Sender Reputation & Sender Score

The sender reputation refers to the reputation of your sending server and more specifically its IP address with ISPs (Internet Service Providers) and ESPs (Email Service Providers) in the context of how likely this IP is to send SPAM. The sender score is a metric that indicates how good or bad your sender reputation is. Think of your send server reputation as the passport to your emails’ success. It’s like a badge of trust that Internet Service Providers (ISPs) look at closely, deciding if your emails deserve to be delivered or not. 

It usually takes time to build a good sender reputation. Imagine that you set up a fresh new server with a brand new, clean IP address that has never been in use before and this server starts sending a huge volume of emails on Day 1. No one else has ever heard of that IP and suddenly “BOOM” – it’s firing tons of emails out. Kinda unexpected? Who would do that? Well, this is a typical behavior pattern of spammers, which is why most ISPs and ESPs would immediately blacklist the IP address (report it to IP blacklist databases) and consider the emails as spam.

What are IP Address Blacklists?
The integrity of your sender reputation is closely tied to the concept of IP blacklists. These blacklists are maintained by various organizations and are used to flag IP addresses that are suspected of distributing spam, harmful content, or engaging in other questionable email practices. If an IP address or domain is added to these lists, it heavily damages its email deliverability as ESPs and ISPs start sending these emails to the spam folder or even blocking them completely.

So one of the main goals of email service providers like us is to maintain a good sender reputation for our servers and our IP addresses in order to guarantee high email deliverability for our clients. At SiteGround our system administrators carefully monitor our network 24/7 to ensure our IP addresses remain untainted by activities that could lead to blacklisting. They manage multiple sending IP addresses in a pool, carefully building a reputation for each and every one of them so should a blacklisting event occur, they would immediately take the bad IP out and replace it with another one, without affecting the sender score or raising the suspiciousness of the Internet Service Providers and Email Service Providers. By proactively managing our mail servers and keeping our IP addresses clear of spam-related behavior, we boost the likelihood of the email service providers to favorably receive your emails, ensuring they reach your subscribers’ inboxes and support the success of your email campaigns.

Domain Reputation

The domain reputation refers to the trustworthiness of your sender domain as seen by email service providers. Again, this is all about how likely it is that your sender domain causes trouble – sends SPAM, launches phishing and spoofing attacks, etc.

To prevent and block such bad practices, the internet community has developed protocols for domain authentication to help ensure that emails are indeed sent from who they claim to be and that this sender has a good history.

Sender Policy Framework (SPF)

The Sender Policy Framework was the first authentication protocol, developed as a way to prevent email address forgery. It helps identify the mail servers that are allowed to send email for a given domain by adding a list of authorized IP addresses and domains as an SPF record in your domain’s DNS records. 

The SPF allows Internet Service Providers to identify emails from spoofers, scammers, and phishers as they try to send malicious emails from a domain that does not belong to them. When an email is received, the receiving server checks the SPF record by looking up the DNS to see if the sending server’s IP is listed. If the IP address is not authorized, the email can be rejected or sent to the spam folder.

SPF is the oldest protocol and on its own, it does not guarantee enough email deliverability assurance. This is why we’ll now talk about the newer protocols – DKIM and DMARC.

DKIM (Domain Keys Identified Mail)

DKIM comes later on and adds an extra layer of security by placing a unique digital signature on your emails. With it, the domain owner generates a public/private key pair – the public key is published in the DNS records, and the private key is used to sign outgoing emails. When an email is sent, a DKIM signature is added to the message header. When you send an email, it includes this signature, which the receiving servers check using your public key to ensure the message is genuinely sent from your domain and hasn’t been tampered with. This digital signature is a powerful trust signal to email service providers, significantly increasing the likelihood that your emails will be delivered successfully. 

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

DMARC combines the powers of SPF and DKIM, adding a set of instructions for email service providers on what to do if they encounter an email that fails these checks. It’s like having a security guard who knows exactly what to do with uninvited guests – whether to turn them away at the door or keep an eye on them. 

How Email Authentication Records Impact Your Email Deliverability? 

As you probably see by now, these records are not really needed by the “sender” server but are needed and verified by the recipient email servers. That means the fate of your emails depends on the rules and protocols that many different recipient servers have decided to follow. Some would only care for your DKIM record, while others would require DKIM and SPF… every server may have a different set of criteria for what kind of records an email should have to be considered legit. This is why, to stay on the safe side and make sure you maximize your email deliverability chances, you better set all three of them right.

To help you in this process and make sure your sender reputation and email deliverability do not get hurt we do two things: 

  • Every new client who signs up for our Email Marketing service and whose DNS zone is managed by SiteGround gets all these records automatically set.
  • And for all of you, using the service with or without your DNS being managed by SiteGround, we block the sending of email campaigns from domains that are missing any or all of these records, saving you from hurting your domain and sender reputation until you set them up.

Quality of the Email List

The quality of the email lists you manage refers to the healthiness of the email addresses that also have interest and genuine acceptance to be on your list. If you are serious about your email marketing strategy your goal is to build an email list and keep it clean of valid email addresses that have formally accepted to receive marketing communication from you. 

Once you start sending out an email campaign you will notice that different things happen with your message depending on the status of the email address and the behaviour of the recipient

  • Some emails bounce back because the addresses are invalid and never get to the subscribers’ inboxes.
  • Some users unsubscribe because they are not interested in receiving any more emails from you.
  • Some users mark your message as SPAM as they did not give an agreement to receive emails from you, because they do not recognize you as a sender, or because you have hit a spam trap.

So let’s tackle each of these problems and their reasons one by one.

Invalid Contacts and Email Bounces

In email marketing, bounces” occur when emails can’t be delivered to the subscribers’ inboxes and are returned to the sender. Bounces are important to monitor in email marketing because a high bounce rate can damage your sender reputation, which can affect your overall email deliverability. There are two main types of bounces:

Hard Bounces 

A hard bounce happens when the recipient server responds that the email address is not valid. This might be an address that used to be active but is no longer, or a wrong email. If you get too many hard bounces the Email Service Providers might suspect you of sending spam because guess who would normally get many hard bounces? Spammers! Another typical behavior of spammers is trying to guess email addresses. They take an organization, dig out a list of employees’ names, and start trying to guess what their email addresses are. In that guess process, they would get a lot of wrong addresses and hence, a lot of hard bounces.

So hard bounces are a big deal, which is why at SiteGround we take immediate action and:

  • We pause email campaigns that start returning too many hard bounces in order to prevent any negative impact on your sender reputation and future email deliverability
  • We “suppress” hard bounce email addresses in your list and will never send emails to them again. This practice not only cleans your list but also keeps your email deliverability rates high, ensuring that your messages are reaching active, valid recipients.

What you could do on top is regularly clean your list from emails that you know are inactive (you have received a notice from the person for example) and browse to clean obviously wrong addresses – missing the domain extension or other elements of the valid email address.

Soft Bounces 

Soft bounces are temporary delivery failures due to issues that don’t necessarily indicate a problem with your mailing list and can happen for a variety of reasons. Let’s look at some common reasons for soft bounces:

  • Subscriber’s inbox is full and cannot accept new messages until some get deleted.
  • Email message is too large – if the email message is too large, the recipient’s server might not accept it. The size limit varies by server.
  • The recipient server is down or offline – if the recipient’s email server is down or temporarily unavailable, the email will soft bounce.
  • Email is blocked by the server – sometimes, the recipient’s server might temporarily block or quarantine the email if it suspects it’s spam or if it’s from a sender that’s been reported in the past.
  • Auto-Responder – if the recipient has set up an auto-responder (for example, an “Out of Office” reply), it might cause a soft bounce.
  • Technical issues – other technical issues with the recipient’s server, such as maintenance or updates, can also cause a soft bounce.
  • Recipient’s server is overloaded – if the recipient’s server is experiencing high traffic or is overloaded, it may temporarily be unable to accept incoming emails.

When these soft bounces occur, different email service providers may take different actions. At SiteGround we do not give up, but have a strategy to make multiple attempts to resend the email, starting with more frequent tries in the first few hours and then tapering off. This retry system is designed to deliver successfully your email campaign as soon as possible, ensuring it stays on track and reaches your subscribers’ inboxes in a timely manner. We aim to optimize email deliverability while maintaining the momentum of your email marketing efforts. 

Users Unsubscribe 

That one is good! Unlike the hard bounces and the spam complaints, having a recipient unsubscribe is not dangerous, but actually healthy – better these not be in your list, deteriorating the quality and engagement rates of your email campaigns. As your email service provider, SiteGround will automatically take all unsubscribed contacts off your list and won’t send future emails to them.

All that being said, it is important that you monitor the unsubscribe rate of your email campaigns. If it is too high or varies, this is a clear signal that the users react badly or positively to the content of the email campaign and you should consider the following: either eliminate from your emails content that leads to higher unsubscribe rates or segment your list so that you serve different audiences with different types of content that they find relevant. 

Emails Get Reported as SPAM

Your sender reputation and email deliverability get really hurt when too many of your emails start hitting the spam folder. At this point, we know the IP address is not blacklisted and we have a solid server and domain reputation so we are crossing these factors out. We are now looking into reasons related to the quality of your email list and your recipients’ behavior.

  • You are hitting spam traps

A spam trap is an email address that looks like a real one but can’t be used for any kind of communication. Most commonly, these are previously active email addresses that are repurposed, addresses with mistyped domains, or emails created on purpose as traps – all of these could get embedded in websites by ISP providers and other organizations intending to catch spammers who scrape websites for contacts. 

The “spam traps” might get your IP address blacklisted in a blink so make sure you avoid and clean those. The spam trap emails will never engage with your messages so to get rid of them a good rule of thumb is to clean all contacts that are older than 3-4 months and never opened your emails. It is also recommended to never scrape sites for emails and never buy email lists.

Last, but not least, add a double opt-in to your forms so that you do not allow spam traps to enter your email lists in the first place. This method requires new subscribers to confirm their email addresses before being added to your list, which requires actual human interaction that spam trap emails would never engage in. Double opt-in forms ensure that you’re only adding valid, engaged subscribers who truly want to receive your emails.

  • The recipient did not accept to be on your list

If you have contacts on your list who did not willingly sign up to receive emails from you, they are very likely to report your message as SPAM. That is why we mentioned earlier that you have to manage the quality of your email list and make sure that you get acceptance from your contacts before putting them on the list. 

  • The recipient clicked “Mark as Spam”/Report Spam/ button instead of unsubscribe

Even if a user has agreed to enter your mailing list, they might still report your message as spam. Psychologically, many people get irritated when they do not see an easy way to opt out of your communication and take a shortcut reporting the message as spam, not considering what this might do to your domain reputation. The cure – make sure you have an easy Unsubscribe form.

There are several things you can do in order to avoid your emails going to spam and your sender reputation getting hurt in the process.


In different parts of the world, different laws require email marketers to receive explicit consent for sending emails through their signup forms. These regulations aim to protect the recipients, but you may want to see them as a good thing for your domain and sender reputation as well – complying with such local regulations tremendously improves your email deliverability rates and makes sure your email list is largely compiled of valid and engaged contacts. Some of the laws that you should consider when making sure you are compliant are the GDPR law in the EU countries, the CAN-SPAM Act, PERC, HIPPA, and others, depending on which country you are targeting and what type of content you will be sending.

Streamlining the Unsubscription Process

A seamless and straightforward unsubscribe process is essential for any email marketing campaign, not just for avoiding spam or legal compliance, but also for upholding a list of truly interested subscribers. An accessible opt-out option is crucial for maintaining the health of your subscriber list and ensuring the accuracy of your engagement metrics.

All email campaigns sent through the SiteGround Email Marketing tool automatically get an easy unsubscribe link in the footer of the emails. As of March 2024, after Google and Yahoo made it a rule that all marketing emails must have a one-click unsubscribe option, we have embedded the 1-click unsubscribe option by default in all email headers sent through our tool and our clients are now automatically compliant with latest deliverability requirements by the big email providers. 

Spam Complaint Management

The moment a recipient marks an email as spam, it sends a negative signal to email service providers, which can harm your domain and sender reputation. To proactively manage this, we automatically remove contacts who have marked your emails as spam from your list. Furthermore, if your email campaigns hit the spam folder too many times, we take immediate action. If the excess occurs mid-campaign, we halt the sending process to prevent further damage. For instances where the issue is identified post-campaign, we mark the campaign as having surpassed the acceptable spam complaint rate and keep a record of the occurrence. Should such overages re-occur, we may block your account from sending further email campaigns through our Email Marketing Tool.

This policy serves a dual purpose: to prevent future email deliverability issues for you as an email marketer and to maintain the high standards of our email servers. By enforcing these measures, we not only protect your domain and sender reputation but also ensure the continued health and reliability of our email infrastructure for all users.

If you’re receiving a high number of spam complaints, though, it’s time to review your content and list management practices. This takes us to the next factor in email deliverability – email content.

Email Content 

The actual content of your email, along with the skill of writing marketing emails, starting with the subject line and body, is a major factor that impacts the spam complaint rate, your sender reputation, and overall email deliverability. Let’s get into some specifics and what to consider when preparing your email campaigns in order to avoid successfully spam filters.

  • Avoid spam trigger words: certain words and phrases are morley to trigger spam filters and send your email to the spam folder. Words like “free,” “guarantee,” and “no obligation” should be used sparingly. Keep your language natural and avoid overly salesy or sensationalist language.
  • Personalize your emails: personalization can significantly increase engagement, which in turn might result in fewer people unsubscribing or marking your email as spam and overall can improve your sender reputation. Use your subscribers’ names and tailor content to their interests whenever possible. Segmenting your list based on your subscribers’ interests or other data that you have about them is highly recommended to increase your email relevancy and engagement.
  • Maintain a consistent schedule: stick to a regular email schedule, which helps subscribers know when to expect your content. Consistency in sending times can build a pattern of engagement that signals to email service providers your communications are expected and valued, reducing the risk of sending your messages to the spam folder.
  • Keep a good text-image ratio: cluttered emails with too many images, fonts, or colors can be off-putting. Aim for a professional, clean design that enhances readability and doesn’t overwhelm the recipient.
  • Watch your grammar: typos and grammatical errors are not just unprofessional – they can also trigger spam filters. Always check your emails carefully before sending them out.
  • Optimize for mobile: a significant amount of emails are opened on mobile devices. Ensure your emails are mobile-friendly with a responsive design so that they’re easily readable on any device.
  • Include a clear CTA: be clear about what you want the recipient to do next. A single, prominent call-to-action can improve click-through rates and engagement.
  • Test your emails: always test before you send out your campaign. Broken HTML and links could also trigger spam filters and have a negative impact on email deliverability.
  • Conduct A/B testing: This helps you identify and fix issues that could affect email deliverability and gives you insights into what resonates best with your audience.

Preventive Email Campaign Checks by SiteGround

When it comes to your email content that’s entirely on you. Still, we know that many clients do not have much experience with email marketing, and navigating between spam filters, compliance, bounces and the whole matter of email deliverability is quite overwhelming. That is why, we give you a hand in controlling the potential level of risk that your emails hit the spam folder. 

Before sending any campaign, we use advanced AI technology to examine it for any signs of spam, phishing, or content that violates our usage policies and evaluate the likelihood of your emails being delivered successfully, and not dreaded in the spam folder. If any issues are detected, our team steps in to manually review them and if needed, stop the campaign and alert you.

For new users of our Email Marketing tool, we go the extra mile by manually reviewing the first three email campaigns. This careful examination aims to reduce the chances of email bounces or spam filter triggers, thereby safeguarding your sender reputation and ensuring high email deliverability as a flying start of your email marketing efforts.

The Road Map To Email Success 

Mastering the art of email deliverability is not a one-time task but an ongoing process that requires attention to detail, adherence to best practices, and a proactive approach to managing your email marketing efforts. From ensuring robust email infrastructure and maintaining a strong sender reputation to keeping your email list clean and crafting engaging content, every step is crucial in reaching your subscribers’ inboxes successfully.

At SiteGround, we are committed to equipping you with the tools, knowledge, and support to navigate the complexities of email deliverability. With our state-of-the-art infrastructure, anti-spam solutions and practices, and continuous management of sender reputation, we ensure that your email campaigns have the best chance of reaching their intended destination. Whether you’re just starting out with email marketing or are an old hand at it, deliverability is king when it comes to campaign success. Maximize the success of your email marketing efforts by selecting SiteGround Email Marketing and make every email count!

Svetoslava Ivanova

Digital Marketer

Enthusiastic about adopting new ways of storytelling Gen Z-er who lives and breathes digital marketing.

Comments ( 1 )

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Fernando Karanga

Mar 29, 2024

Nice info


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