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Email Deliverability Guide: How to Guarantee Your Emails Get Delivered

email deliverability cover image with an email keyboard button

Email deliverability indicates the likelihood that an email you send will actually reach your subscriber’s inbox instead of reaching the spam folder.

This simple definition doesn’t do justice to just how complex email deliverability is. And that’s exactly why our deliverability guide is the only one you need to read — we’ve covered every aspect of deliverability you need to know. From authentication protocols and technical requirements to email list management and campaign content creation, we’ve covered it all.

If you’ve ever wanted to learn the inner workings of email deliverability, you’ll find all the answers below.



What is Email Deliverability?

In email marketing, senders run campaigns in which they send millions of emails to their subscribers. But how many of these land in the primary inbox? If you want your subscribers to open your emails and click on your links, they must be able to see your messages first. And that’s less likely if your sendings end up in any other folder. 

This is exactly what email deliverability refers to — the ability of an email to reach the inbox instead of getting deleted or marked as spam.

Why does it matter?

Because if your emails don’t reach the inbox, your open rates, click-through rates, and overall campaign effectiveness will suffer.

Several factors affect deliverability, and we are going to cover them systematically. 

Email deliverability depends on three pillars:

  1. Sender reputation,
  2. Strategy,
  3. Technical setup.

By paying close attention to all the aspects of these three foundational elements, you should be able to achieve your best deliverability rates.

Let’s get right to it!


The First Pillar of Email Deliverability: Sender Reputation

The simplest way to explain sender reputation would be to use the example of credit history. Similar to your history of spending and settling payments, there is a record of how you have behaved in the past as an email sender. 

If the sender’s history records sending legitimate, high-quality emails that recipients engage with, they build a good reputation. However, if a sender is known for sending spam, or their emails often get marked as junk, their reputation suffers.

What Affects Sender Reputation?

Sender reputation is dictated by these aspects:

FactorsEffect on sender reputation
Bounce ratesA bounce happens when an email can’t be delivered. Has a strong negative impact on sender reputation. 
Engagement metricsHigh open rates, click-through rates, and low unsubscribe rates all signal to ESPs that your emails are relevant. Conversely, high complaint rates can significantly hurt your reputation.
IP reputationSender reputation isn’t just about your email address itself, but also the reputation of the IP address you’re sending from. 
Domain reputationA history of spam complaints associated with your domain name can negatively impact your sender score.
Sending practicesESPs look for consistent, targeted sending. Sudden spikes in email volume or sending to purchased/outdated lists raise red flags.
Spam traps and blacklistsIf your emails end up in spam traps or on industry blacklists, it’s a major blow to your sender reputation.
Email authenticationSPF, DKIM, and DMARC are email authentication protocols that verify you’re a legitimate sender.
Sender reputation: Understanding its components

Addressing Sender Reputation

To manage your sender reputation effectively, it’s important to:

  1. Monitor your analytics and campaign performance,
  2. Track domain and IP reputation, 
  3. Be rigid about list quality, 
  4. Send relevant content at the right volume and frequency,
  5. Choose a reputable ESP.

We will now break down each of these points to help you unlock the best sender reputation. 


What Do Your Metrics Say About Sender Reputation?

There’s a lot you can learn by scrutinizing your campaign metrics.

Negative reactions by recipients are the most harmful; they affect your sender reputation. Spam complaints are the most dreaded because they start to cause problems after your complaint rate exceeds 0.1%.

Your ESP dashboard can tell you a lot about the performance of your email marketing campaigns.

These performance metrics are the most critical:

MetricDefinition
Delivery RateNumber of emails delivered to recipients’ mail servers of total sent emails.
Open RateNumber of recipients who opened the email divided by total sent emails.
Click-Through Rate (CTR)Percentage of recipients who clicked on at least one unique link within the email.
Bounce RateOf the total sent emails, the number of emails that could not be delivered.
Unsubscribe RatePercentage of recipients who opted out of the mailing list after receiving an email.
Spam ComplaintsNumber of recipients who marked the email as spam.
Conversion RatePercentage of recipients who completed a desired action after clicking a link in the email.
Email marketing metrics explained

 Of these, the spam complaint rate is a metric you should pay careful attention to. Exceeding a 0.1% spam complaint limit can result in being flagged as a spammer by mail providers.

Performance Metrics and Their Influence on Sender Reputation 

Here’s what the different metrics tell you about email performance:

Metric TrendWhat does it tell you about campaign performance?
High open ratesThe content is effective, and links/CTAs are relevant.
High CTRThe content is effective and links/CTAs are relevant.
Low unsubscribe ratesIndicates subscribers are engaged with your content and want to keep receiving your emails.
Low bounce rateYou have a clean email list and aren’t sending to uninterested recipients.
Low complaint rateMost critical for sender reputation; it means readers don’t consider your content spam.
What metrics tell you about your sender reputation 

By closely tracking engagement metrics, you can work towards achieving better email deliverability. 


Domain and IP Reputation: The Core of Sender Reputation

Domain reputation and IP reputation are two sides of the coin when it comes to email deliverability. They both influence whether your emails land in the recipient’s inbox or the spam folder.

Understanding Domain Reputation

Several factors affect domain reputation, including:

  • The age of your domain: Established domains generally have a better reputation than newly registered ones.
  • Email authentication practices: The use of SPF, DKIM, and DMARC helps verify you as a legitimate sender and improves trust with ISPs.
  • Spam complaints: If recipients frequently mark your emails as spam, the damage extends to your domain reputation.
  • Content and list quality: Sending relevant emails to engaged subscribers reflects positively while sending spammy content or to uninterested recipients can damage your reputation.

A good domain reputation means your emails are more likely to reach inboxes. A poor reputation can lead to stricter filtering or even blacklisting by ESPs. 

You have more control over your domain reputation compared to your IP reputation(in the case of shared IPs). 

IP Reputation Explained

An IP address reputation is influenced by:

  • Sending activity of other users sharing the IP: If other senders using the same IP have a history of spam, it can hurt your reputation even if you’re following best practices.
  • Spam complaints: Similar to domain reputation, complaints about emails sent from the IP will negatively affect its reputation.
  • Inconsistent email volume: A large increase in emails sent from the IP can raise red flags for ESPs.

Remember — using a shared IP address from a reputable ESP is better than using a dedicated IP. This is because the ESP’s good reputation can positively influence your IP reputation.


List Quality: Your Sender Reputation Depends on It

Your email list quality refers to the overall health and engagement level of your subscriber list —the quality and relevance of the addresses on it. A high-quality list consists of engaged subscribers who are genuinely interested in your content.

List quality is possible by sticking to these guidelines:

Of these steps, the last one is likely the most crucial one. 

Segment Your Lists

This table explains the benefits of segmenting your email lists diligently:

BenefitThe positive effect
Increased engagementWhen subscribers receive emails about their interests and needs, they’re more likely to engage with the content
Improved ROITargeted emails with relevant offers are more likely to convert subscribers into paying customers.
Reduced unsubscribesSegmentation ensures your audience gets the content they signed up for, reducing unsubscribes.
Better sender reputationHigher engagement metrics have a positive impact on your sender reputation.
Segmenting email lists: Advantages

Once you have your list segmentation strategy in place, it’s time to focus on your email content.


Email Content and Volume: Hallmarks of a Good Sender

Email content is a critical factor in protecting sender reputation and improving email deliverability. 

When you send irrelevant email content, readers get annoyed; such reactions affect your sender reputation. Spam complaints are the worst because they cause problems once your complaint rate crosses the 0.1% threshold. But mailbox providers also use other methods to track reader interest — they pay attention to indicators of disinterest, such as unread emails being deleted.

In the past, email marketers used bad email marketing practices like adding a huge number of inactive subscribers to their email lists. This would drive down their complaint rates, but it caused mailbox providers to pay attention to other aspects like positive reactions or engagement of subscribers. 

ISPs even track user behavior, such as scrolling, starring, or forwarding, to assess interest in the emails. Email marketers, of course, can’t access such data.

As far as protecting sender reputation goes, poor engagement rates are as much of a problem as high complaint rates. So next, let’s go over best practices for email content so you can achieve the best metrics.

Best Practices for Email Content

These 9 guidelines for email content will ensure you hit the sweet spot every time:

  1. Subject line: Keep your subject line at 50 characters or less to ensure it displays fully on most devices.
  2. Preheader text: Utilize the preheader text to provide additional context.
  3. Relevant content: Provide valuable content that informs, educates, or entertains your audience.
  4. Email personalization: Whenever possible, personalize emails with the recipient’s name, location, or other details to make them feel more targeted.
  5. Email tone: Depending on the topic, use the right email tone.
  6. Call-to-action (CTA): Use a powerful CTA. Tell subscribers what you want them to do next, whether it’s visiting a landing page, making a purchase, or downloading a resource.
  7. Visible branding: Use consistent colors, fonts, and logos to build brand recognition.
  8. Aesthetic design: Avoid cluttering your email with too many elements.
  9. Unsubscription options: Always include simple unsubscribe links for readers to unsubscribe from your list.

Email Volume and Frequency

Sending too many emails is a bad idea; it’s an equally bad idea to send too few. 

While sending excessive emails risks a higher unsubscribe rate and spam complaints, sending emails infrequently causes its own set of issues.

  • Subscribers will forget about you and ignore your emails/mark them as spam.
  • ISPs take note of your low frequency and flag you.
  • Identifying inactive subscribers becomes challenging.

Using a shared IP address is a good way of avoiding some of those risks. When you use a shared IP address, mailbox providers may see you as a high-volume sender, as your email volume is clubbed with other senders’ using the same IP address.

In general, it’s a good idea to send at least one marketing email a month.

Avoid Spam Triggers

When filtering emails, ISPs used to weigh factors such as subject lines, spammy words, poor formatting, and excessive images. They have moved on from these to more technical indicators. We still recommend avoiding exclamation marks and all caps or using spam trigger words in your emails. 

Mailboxes have now switched focus to the coding of your marketing emails. A badly coded HTML email is far more likely to set off spam alarms. Excessive comment tags can also look suspicious because they seem like an attempt to hide spam content.

Spam filters are particularly sensitive to HTML forms, JavaScript usage, Flash elements, and tags, such as <object> or <embed>. This is due to their ability to conceal malicious code. ISPS may block or mark your email as spam if they detect such issues.

Be cautious when linking — do not link to suspicious sites. It’s also recommended that you use full URLs instead of link shorteners. 


Your ESP: The Final Piece of the Sender Reputation Puzzle

Your domain and IP reputation will not be the only factors determining your deliverability rates — your ESP also plays a big role. 

This table explains the critical role played by your ESP:

AspectHow you benefit
Focus on deliverabilityA reputable ESP has advanced deliverability features and services.
Relationship with ISPsGood ESPs maintain good relations with major ISPs. This can help ensure your emails avoid spam folders.
IP reputationReputable ESPs manage their IP addresses diligently; this includes both dedicated IP addresses and well-managed shared IPs.
Compliance Reputable ESPs stay up-to-date on anti-spam regulations like CAN-SPAM and GDPR.
Spam filteringESPs have sophisticated spam filters to prevent spammers from using their platform. Some ESPs even offer spam-testing tools.
Robust list management toolsGood ESPs provide tools to manage your email lists effectively; such tools help reduce bounce rates and spam complaints.
Analytics Reputable ESPs have detailed analytics and reporting features to help you monitor key metrics.
Feedback loopsReputable ESPs often participate in feedback loops with major ISPs. This data helps you refine your list and your content strategy.
Reputed ESP: Deliverability benefits

A reputable ESP is your partner in achieving the inbox placement rates you desire. And that’s why so many users have switched over to Campaign Refinery — we have the best deliverability rates in the biz. We’ll tell you a lot more at the end of the article!

Now that we’ve covered sender reputation in detail, we can move on to the next pillar which dictates how your emails perform in terms of inbox placement.


The Second Pillar of Email Deliverability: Strategy

How you execute your email marketing sends plays a huge role in your deliverability rates. Your strategy needs to be better than firing off campaigns to a random list of contacts. You need a game plan — an understanding of human psychology plus excellent knowledge of your product. 

Curious to learn applicable steps for email marketing strategy? 

It’s different for broadcast emails and email campaigns, as you will see in the upcoming sections.


Broadcast Emails: Strategy

Broadcast emails are one-time messages sent to a large group of subscribers. 

Good examples of broadcasts would be: 

Broadcast emails are often sent in a way that they reach a wide audience simultaneously. They are useful for sharing general information or time-sensitive content with a large audience.

Much of broadcasting success has to do with audience segmentation. To segment effectively, you must organize by factors like where they opted in from, their purchase history, and what links they’ve clicked on in the past. 

You also need to filter down based on recent engagement levels. For this, you can use data such as opens, clicks, purchases, or website visits from recent history. Filtering down based on engagement is one of the fastest ways to signal to email providers like Google, Yahoo, or Microsoft that you are focused on the quality of your subscribers. It also shows that you are delivering the content your subscribers desire.

This combination of factors — recency of engagement, recent interaction,  and opt-in source — is going to yield much higher engagement rates from a percentage standpoint. This will signal to ISPs that you are a high-quality sender, elevating your sender domain reputation and improving future inbox placement rates.

This improved placement has a counterintuitive result; sending to fewer (yet more relevant subscribers) will actually yield a net increase in total opens and total clicks, not just from a percentage standpoint over time.

In short — sending to fewer people, while reducing the number of emails you send, will actually yield superior results, in terms of conversion rates. Everything else being equal, sending fewer emails should actually result in more conversions and increased revenues.


Email Campaigns Need Strategy, too

Email campaigns refer to a series of emails sent over a period of time with a specific goal in mind. 

How well they perform depends on how carefully you designed each campaign. We’re going to let you in on how the pros approach this bit.

Creating a Strategy for Your Campaigns

Some campaigns are more strategic and structured, often involving multiple emails to nurture leads, engage subscribers, or drive conversions. These campaigns are typically automated (but can be manual) and are designed to guide recipients through a customer journey

When you send campaigns, you set a precedent for what subscribers can expect from you in the future. You can also create automated experiences based on actual subscriber engagement — this helps quickly weed out unengaged recipients.

Campaigns should be delivering on a specific promise towards a specific outcome. Everything you send within a campaign should in some way, shape, or form support this journey for the subscriber.

You must create automation flows to rapidly unsubscribe unengaged subscribers who don’t open and click your campaign emails after a few emails are sent. This is a great way to significantly increase the quality of your list, boost your domain reputation, and reduce wasted resources.

Secondarily, you can use campaigns to deliver “just in time” experiences to any subscriber who takes certain actions, like clicking links. You can identify them as “high intent” and plan campaigns to target this segment. This way, you can deliver your pitch to those who are most interested and there’s a chance they will take explicit actions, signaling they want to know more.

When designing campaigns this way, you drastically reduce your risk of spam complaints. 

Campaign strategy is clearly different from broadcast email strategy, where you pitch to every subscriber. Instead, use broadcast emails as a ‘filter’ to see who engages, and then use a combination of campaigns and intelligent automation flows to follow up with subscribers who have high intent.

Interesting how strategy dictates your deliverability, right? All you need now is to understand the technical setup — the final pillar.


The Third Pillar of Email Deliverability: Technical Setup

As email evolved, so did spam. Since the volume of spam and other fraudulent email has gone up, security measures have improved and there are numerous steps email marketers have to take to ensure their email marketing setup is correctly configured.

This pillar can be broken up into 3 sections:

  1. Implementation of authentication protocols, 
  2. Using SSL/TLS,
  3. Warming up your domain.

The most important one is the correct configuration of protocols that use your domain’s DNS records to verify the legitimacy of an email and its sender. 


Authentication Protocols: Essential for Good Deliverability

As email became a primary communication tool globally, it also became a target for malicious actors who exploited its initially trust-based system. Such individuals could easily spoof email addresses by impersonating users or domains to send fraudulent messages. 

To address these security issues, authentication protocols were created.

What do SPF, DKIM, DMARC, and BIMI do?

First, let’s understand the role played by each protocol:

ProtocolPurposeHow it functions
SPFTo prevent sender address forgery by verifying sender IP addresses.SPF records specify which IP addresses are allowed to send mail for that domain. 
DKIMTo ensure the content of the emails remains unchanged from sender to recipient.DKIM provides a digital signature that verifies the content has not been tampered with during transit. 
DMARCIt allows domain owners to protect their domain from unauthorized use.DMARC has a reporting function that sends authentication data to the sender.
BIMITo display brand logos next to authenticated emails in inboxes.BIMI allows domains to display their brand logo in supported email clients. It builds on DMARC security.
Email authentication protocols: What do they do?

Implementing these requires technical configuration; you can get help from your ESP. But the benefits of increased trust, reduced spam, and improved inbox placement make it worthwhile!


Using TLS is a Must for Inbox Placement

SSL or TLS (Transport Layer Security) encrypts the communication channel between your email server and the recipient’s server. This encryption scrambles the content of your emails, making them unreadable to anyone who might intercept them in transit. 

The benefits of TLS implementation include:

  • It ensures the sensitive content of your emails, such as customer data or special codes, remains confidential.
  • By encrypting emails, TLS safeguards them from unauthorized access or tampering during transmission. This is critical for brand reputation and prevents attackers from modifying your content for malicious purposes.
  • While not a part of the TLS protocol, DKIM relies on a secure TLS channel to function correctly.
  • Many ESPs consider the use of TLS a positive indicator of sender reputation. Consistently sending emails with TLS encryption can potentially improve your deliverability.

TLS is an essential layer of security for email marketing and consistent deliverability.


Warm Up Your Domain: A Critical Phase of Setting Up Email Ops

Warming up an email domain refers to the process of gradually increasing the volume of emails sent from a new domain over a while. 

This practice is essential for building a positive reputation with ISPs and ensuring superior email deliverability. Not doing it has negative effects, too — sudden spikes in email activity from a new domain can trigger spam filters, leading to emails being blocked or sent to the spam folder. Warming up helps avoid these triggers by showing consistent and responsible email practices.

How to Warm up an Email Domain

Remember, to warm up your domain, you must focus on sending high-quality, engaging content that resonates with your audience.

High open rates and click-through rates signal to ESPs that your emails are valuable and relevant, further improving your sender reputation.

Here’s a step-by-step guide to warming up your email domain:

  1. Before you begin, ensure your domain is set up with SPF, DKIM, and DMARC.
  2. Next, ensure your email list is clean and up-to-date. Remove any invalid addresses to minimize bounce rates.
  3. For better results, segment your email list. Prioritize engaged subscribers who have recently interacted with your brand or signed up for your list.
  4. For the first 2 weeks, start with a low volume of emails — maybe a few hundred per day — and gradually increase the volume over time. Be as consistent as possible.
  5. If you see increased bounce rates or spam complaints, slow down the ramp-up process.
  6. If you’re happy with the results of the first couple of weeks, gradually increase sending volume. You can also include new segments, but prioritize those who have shown some level of engagement.
  7. For the next 2 weeks, ramp up your email volume. Continue monitoring your metrics and adjust your sending pace as needed.

Consistency is key throughout the warm-up process. By following these steps and maintaining a strategic approach, you can effectively warm up your domain and ensure you achieve the best deliverability rates.

Speaking of the best deliverability rates…


Campaign Refinery: The Ultimate Email Deliverability Solution

If you’re seeking the best inbox placement rates, then Campaign Refinery is the obvious choice for a very simple reason: we have the best deliverability rates in the industry.

Email deliverability is our #1 focus; everything we do here at Campaign Refinery is concentrated on this one goal.

Our clients enjoy additional, high-value features that help them achieve top-tier inbox placement:

  • Automated list-cleaner: We have an automated list-cleaning tool that removes all invalid emails (including spam traps, role emails, temporary emails, complainers, etc).
  • Screening new customers: We require all clients to go through a vetting process before they can join. Our shared IP pool enjoys a top-tier reputation! 
  • Powerful automation: Email marketers deserve the best automation designers — so we added it to our platform. 
  • Gamification: Want engagement? Try our Gamification feature, which rewards your subscribers using a points-based system. It has managed to clock open rates of 76.37% and click rates of 72.76%!
  • Spam monitoring: We constantly monitor our servers for signs of spammy activities. 
  • Tag-based system: Hyper-refine your audience with our tagging features — the future of targeted emails is here!
  • Integrated Google Postmaster Tools: Soon, we will add Google Postmaster Tools to the analytics dashboard. Get stats on your Gmail users directly from the source!

Campaign Refinery is all about elite email performance. 

Apply to become a customer today and achieve the deliverability rates of your dreams!

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