The Ultimate Guide to Email Deliverability in 2023

(In 55 Steps)

by Merve Civelek

Do you ever thought like this...

Crafting valuable content, devising attention-grabbing subject lines, and pinpointing the timing to send your emails almost sound like setting up a creative pipeline!

It's ok if you've never thought like that before. Infact, nobody does, expect if you happen to be an email deliverability expert (ahem!).

Let's continue...

Where I'm heading is; the very things are happening with the pipes is also happening with email deliverability, this entire process could hit a roadblock if your emails get clogged along the way and do not flow smoothly into your subscribers' primary inbox.

For a second, just imagine being a skillful plumber setting up a network of pipes to deliver water to various locations. Just like crafting engaging emails, you carefully assemble the pipes, making sure they're sturdy and well-connected. 

But if there's a blockage, a filter, or a leak along the way, the water will not reach its intended destination, no matter how well you've set up the pipes.

This is similar to email deliverability.  

If your emails encounter obstacles like spam filters or promotions tabs, they won't make it to your subscribers' primary inbox, and your efforts might go to waste.

Today, I'll do my best to explain all the major aspects of deliverability in layman's terms.

Yet, email deliverability is made up of a complex network of interconnected pipes. However, don't fret just yet!

Even if you're not a technical person, as long as you rely on your email list to generate revenue, you should be able to walk away with a solid understanding of email deliverability – knowing what to do and what not to do to ensure your emails always flow smoothly to where they belong; the Primary Inbox.

5 main pillars of Email Deliverability

Authentication, Reputation, Infrastructure, Content and Other factors are what makes up overall email deliverability.

Let's dive into them!

#1st Pillar: Email Authentication

Email authentication is like a digital ID card for your emails, ensuring they're genuine and trustworthy. Just as you show your ID to prove you're you, email authentication proves your emails are really from you. This is important because spammers can pretend to be you, sending fake emails that look real. Email authentication adds layers of security to prevent this.

Ok, do not let the following acronyms scare you, I promise you they will make sense after you read them!

1. SPF (Sender Policy Framework):

Think of SPF as your email's travel plans. When you send an email, SPF tells the recipient's email provider which servers (travel plans) are allowed to send emails on your behalf. This way, they know your email is authorized and not a sneaky impersonator. 

You want to include all of the domains that you're sending emails from. Though there are restrictions around that, maximum is around 4 senders, just to be on the safe side.

2. DKIM (DomainKeys Identified Mail): 

DKIM is like putting your signature on the email. When you send an email, DKIM adds a unique digital signature that's verified by the recipient's server. This signature proves the email wasn't tampered with during its journey.

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

DMARC is like your email's bodyguard. It sets rules for how your emails should be handled. If an email fails SPF or DKIM checks, DMARC helps decide whether it's allowed in or gets rejected.

Make sure to set this up "only" after being sure your SPF & DKIM setting are correct, otherwise you'll end up sending your own emails to spam folder!

Why Email Authentication Matters

Image by jcomp on Freepik

Ok, here's an another analogy for you to keep things simple as promised (:

Imagine you're inviting friends to a party. You want to make sure they know the invitation is really from you, not someone else playing a prank.

Email authentication works the same way. It prevents cyber "party crashers" from sending fake emails that look like they're from you. This keeps your emails safe and helps maintain your reputation as a trustworthy sender.

So, in your case, when you send out a special discount offer to your customers, without email authentication spammers could pretend to be you and send fake offers.

But with SPF, DKIM, and DMARC, your customers' email providers know it's really you sending the offer. Your emails stand out in their inboxes, and customers can trust the deals you're offering.

In essence, email authentication is your email's security guard, making sure it's allowed into the recipient's inbox without any doubts about its authenticity. Just like a valid ID ensures your entry to a secure event, email authentication ensures your emails are welcomed and trusted by recipients' email systems.

This authentication step is crucially important for email deliverability, as mail providers like Gmail, Hotmail, and etc. use this as a first step to filter out any suspicious looking senders, hence their emails. Their AI generated filters are so good, those kind of emails do not even end up in Spam folder, they just disappear...

#2nd Pillar: Sender Reputation

What's Sender Reputation? It is like the online image of the email address you use to send your emails. Think of it as a scorecard that rates how trustworthy your emails are.

Mainly, your sender reputation is calculated on a scale of 0 to 100.

But how does sender reputation really function? What things make it go up or down?

Here's the things that effect your Sender Reputation: 

  • The number of emails sent from your domain 
  • The number of emails sent from your ESP's IP address
  • How many emails you send each day
  • The overall number of emails you've sent over time
  • And the overall holistic history of engagement that happened between your subscribers & those emails

What Are The Factors Influence Sender Reputation?

4. Engagement Metrics: 

The level of interaction your recipients have with your emails, such as opening them, clicking links, and replying. High engagement indicates that your emails are relevant and valuable to your audience, which contributes positively to your sender reputation.

5. Spam Complaints: 

When recipients mark your emails as spam, it signals that they didn't find your content useful or wanted, or sometimes they are not able to unsubscribe so they hit the spam!

Frequent spam complaints (in fact, 1 out of 1000 is enough to end up in spam!) can lower your reputation, as email providers interpret these as signs of unwanted emails.

6. Bounce Rate: 

This refers to the percentage of emails that couldn't be delivered to recipients due to invalid or non-existent email addresses.

Sometimes people sign up with fake emails to get the incentive only, sometimes there is a typo, sometimes they stop using that email, and sometimes those inactive emails are owned by mail providers as spam traps to see if your emails will end up there (hence the name implies; as a trap).

All of them cause high bounce rates, which indicate poor list hygiene and will impact your sender reputation negatively.

7. Unsubscribe Rate:

The rate at which recipients opt out of receiving your emails. An excessively high unsubscribe rate might indicate that your content isn't meeting their expectations, leading to a potential reputation decline. 

Usually, this happens in spikes based on a specific campaign you've sent. To be able to detect those, you better watch them closely. And make sure to have a system that removes those subscribers from your list right away. 

8. Blacklist Listings: 

Being listed on email blacklists indicates suspicious or spam-like behavior. Email providers reference these lists to assess the credibility of your emails, so being on a blacklist can significantly harm your sender reputation.

Blacklists are like the bouncers at the club entrance, checking their list to see if you can enter or not. Though there are +100 blacklists out there, not all of them are dangerous.

Here are the 7 email blacklists you should be aware of:

  • Composite Blocking List (CBL)
  • Spamhaus Block List (SBL)
  • XBL Exploits Block List
  • Spamcop
  • Passive Spam Block List (PSBL)
  • Invaluement
  • Barracuda

9. Content Quality:

It sounds cliché, but the relevance, value, and authenticity of your email content matter. If recipients consistently engage positively with your content, it reflects positively on your sender reputation. In fact, positive engagement is the only true north star for email providers like Gmail, when it comes to deliverability.

10. Frequency:

How often you send emails can influence reputation. Sending too frequently might lead to recipient fatigue, resulting in a lower reputation if engagement drops due to overwhelming frequency. 

In fact, I do recommend daily emails; however, you better do this in progress. And avoid sending a high volume of emails outside of your regular email sending cadence. Such spikes are not welcomed; neither by subscribers nor email providers.

Maintaining a High Sender Reputation

11. Use Permission-Based Lists:

Only send emails to people who've given explicit permission to receive them. Avoid sending unsolicited emails, as they're likely to lead to complaints and reputation issues.

12. Monitor Engagement Metrics:

Regularly track metrics like open rates, click-through rates, and replies. Understanding how recipients engage with your emails allows you to adjust your strategies and maintain positive interactions. You can check those through your ESP's dashboard.

13. Handle Complaints Promptly:

If recipients complain about your emails or request to unsubscribe, address their concerns promptly. Ignoring complaints can lead to more severe reputation problems.

14. Regular List Cleaning:

Periodically review and remove inactive or bouncing email addresses from your list. A clean and engaged list positively impacts sender reputation. You can use such tools like Never Bounce, to get it done for every quarter.

15. Avoid Spam Triggers: 

Stay away from practices that trigger spam filters, such as using excessive capitalization, exclamation points, or deceptive subject lines. Sending content that genuinely matches your subject lines enhances your reputation.

16. Use Double Opt-In:

Implement a double opt-in process where subscribers confirm their subscription. This extra step ensures that your recipients genuinely want to receive your emails, reducing the chances of spam complaints. Or, ifyou don't want to do this, then you should be very strict with your sunset policy aka not sending emails to people who are not engaging.

17. Authentication: 

Implement SPF, DKIM, and DMARC authentication protocols to verify the legitimacy of your emails. As I've discussed this part above, these measures enhance your sender reputation by ensuring that your emails are indeed from you and not from malicious sources.

What to Do if Your Sender Reputation is Low?

18. Identify the Issue:

Investigate the specific factor(s) causing your low reputation. Understanding the root cause helps you address it effectively. You need to use a lot of different sets of tools for that. I highly recommend signing up for Google's Postmaster tool right away (though before doing that make sure your authentication is set up correctly, otherwise you're asking to get negative feedback).

Also use the following tools to detect possible issues: 

19. Review Content:

Assess your email content for relevance and value. Adjust your messaging to better resonate with your audience. As this is the center point of entire process.

Consider running a re-engagement campaign, which will help you determine subscribers who are still interested in relevant content, as well as filter out those that are not. Setting up a strict sunset policy that will focus only on engaged subscribers will help a lot, until you get your reputation back.

20. Audit Your List: 

Scrutinize your email list for inactive or unengaged subscribers. Removing such recipients helps improve your overall engagement metrics. I recommend suppression for subscribers who are not engaging +90 days.

21. Reduce Sending Frequency:

If your emails are being sent too frequently, consider spacing them out. This can help prevent recipient fatigue and improve engagement.

22. Request Delisting: 

If your domain or IP is listed on a blacklist, follow the instructions provided by the blacklist to request removal. Once removed, your sender reputation can gradually improve.

#3rd Pillar: Email Infrastructure

Think of email infrastructure as systems that work behind the scenes to make sure your emails travel safely from you to your subscribers. It's like the intricate network that ensures your messages are delivered reliably.

Key Building Blocks of Email Infrastructure:

23. Feedback Loops (FBLs):

What it is: Feedback loops are like a helpful alarm system. They let email providers like Gmail to tell you if someone marks your emails as spam. 

Best Practices: Pay attention to these reports. If people complain about your emails, it's important to address their concerns and maybe remove them from your list. You need to be subscribing to each one of those Feedback Loops one by one to get that information directly from those mail providers. (I do take care of this for my clients.) 

Things to Be Careful About: Don't ignore complaints – it can hurt your reputation.

24. Abuse Reporting:

What it is: This is like giving recipients a button to say, "Hey, I don't like this." It helps you understand what your audience likes and dislikes.

Best Practices: Make it easy for people to unsubscribe. When someone reports a problem, try to fix it quickly.

Things to Be Careful About: If you hide the unsubscribe link or don't listen to complaints, email providers might start considering your emails as unwanted, hence put you into the spam.

25. MX Records (Mail Exchange Records):

What it is: MX records are like road signs that tell your emails where to go. They direct emails to the right inbox.

Best Practices: Make sure these signs are set correctly so your emails don't get lost. Feel free to use tools like Check MX, a free tool by Google to help you review your technical foundations.

Things to Be Careful About: If your signs are wrong, your emails might end up in the wrong mailbox.

26. IP Address (Shared vs. Dedicated):

What it is: Your IP address is like your unique digital address. You can have shared one with others by using your ESP's default IP or have your own dedicated IP.

Best Practices: If you send a lot of emails to a lot of subscribers or want more control, consider having your own IP address. 

Things to Be Careful About: Sharing your address with people who send spam can hurt your email's reputation. At the same time, if you're not actively using email marketing (sending less than 50,000 emails per week), then it's better to stick with an already warmed-up and trust-enforced shared IP address of your ESP.

27. Sending Domain (Shared vs. Dedicated):

What it is: The sending domain is like your online nickname. It can be shared with others via using your ESP's default domain name or be just your own domain. Works very similarly to an IP address. Exact same reasonings apply here as well when deciding which way to go.

Best Practices: Having your own domain gives you more control and trust if you're a high volume sender. 

Things to Be Careful About: Sharing your domain with untrustworthy senders can damage your reputation. But also having your own dedicated sending domain without a good amount of volume will take a long time to build that trust that comes with your ESP's shared domain.

28. IP and Domain Warm-up:

What it is: When you're new in town (having a new IP/domain), it's like introducing yourself gradually. Sending too many emails at once will look suspicious.

Best Practices: Start with a small number of emails, especially focus on your most engaged segment, and gradually increase that number based on the engagement. I recommend starting with people who engaged within a 30-day period, then slowly expand it to 60 days, 90 days, 120 days, and finally to the whole list.

This helps build trust with email providers as they will keep seeing every single email you're sending is being welcomed and positively engaged by your recipients. 

Things to Be Careful About: Sending a lot of emails to your entire list too quickly can trigger spam filters. This is the down side of having your own dedicated IP/domain address, make sure to take your time with this warming-up process.

29. Transactional vs. Marketing Emails:

What it is: This is like sorting your clothes – you keep socks separate from shirts. Similarly, keeping transactional emails (like receipts) separate from marketing emails helps ensure they reach their destination without worrying if something smelly happens with your main domain that you use to send marketing emails; it won't affect the domain you're using to send emails for transactional emails.

Best Practices: Keep transactional and marketing emails apart. It keeps your important emails safe. I recommend using a subdomain rather than a different domain name, as you still want to keep things aligned. Also, you can consider having a separate IP address for those emails, depending on your business type and the volume of transactional emails you're sending daily.

Things to Be Careful About: Mixing them up might create confusion around open rates, as transactional emails happen to have very high open rates, up to 80%. So do not involve them when calculating your open rate!

30. Choosing the Right ESP:

What it is: Selecting the right Email Service Provider (ESP) is like picking a reliable travel companion for your email journey. It affects how smoothly your emails are sent, received, and managed.

Best Practices: Some of them have a really bad reputation when it comes to delivery out of so many people using them for free, such as MailChimp (free version). Also, there are some good ones that come with reliable deliverability as long as you're not messing up with your settings, such as Active Campaign, Klaviyo for e-commerce are pretty good options.

Things to Be Careful About: Before considering changing your ESP, make sure to consult an email deliverability expert as it'll be a long process, let's say a couple of months to warm things up and get ready. There are a lot of factors to consider, and all depends on what kind of business you are and the volume of emails you're sending.

#4th Pillar: Email Content

Email content is like the heart of your message. If it's any good, and resonates with your list you'll be making lot of money. Crafting engaging content is essential for grabbing their attention and delivering your message, this time to their hearts & brains (: 

Best Practices and Things to Consider

31. Avoid URL Shorteners: Using URL shorteners, like, might look tidy, but they can trigger spam filters and make your links seem suspicious.

32. Avoid Naked URLs: Sending links as plain URLs without any context or text can appear spammy. Always provide some context for your links.

33. Links Should Sync with Your From Domain: Linking to pages that share the same domain as your sender's & from address builds trust and authenticity. Otherwise, it becomes suspicious

34. Avoid Email Subject Line Malpractices: Using misleading or overly sensational subject lines can result in your emails being flagged as spam. Let's delve into some examples of what to avoid:

  • Deceptive Claims: Subject Line: "You've Won $1,000,000! Claim Your Prize Now!"
  • Misleading Urgency: Subject Line: "Urgent: Last Chance to Save 99% on Your Purchase!"
  • Clickbait Tactics: Subject Line: "Shocking News! You Won't Believe What's Inside!"
  • Inaccurate Personalization: Subject Line: "Exclusive Offer for [Recipient Name] - Don't Miss Out!"
  • Unrelated Content: Subject Line: "Get Fit Fast!" (For a Cooking Recipe Email)
  • Overuse of Symbols and Capitalization: Subject Line: "������!!! Buy NOW!!!"
  • Toxic Keywords: Subject Line: "Meet Singles Now - Hot and Desperate!"
  • Impersonating Trusted Sources: Subject Line: "Your Bank Account Alert: Immediate Action Required"

35. Avoid Spammy Words in Your Email Copy: Words like "urgent," "free," or excessive use of exclamation points can trigger spam filters. Use them judiciously.

36. Do Not Use Free Mail Senders Like Gmail: Sending emails from free email providers will make your emails seem less professional and harm your deliverability. I also say stay away from free ESPs like the free version of MailChimp, as those attract spammers.

37. Relevant Content: Ensure your email content is valuable and relevant to your recipients' interests and expectations. Segmentation comes to play a huge role in here, take advantage of it by analyzing your list in demographically, behaviorally, and geographically. This lets you send targeted content, increasing engagement and relevance.

38. Plain Text Combined with HTML: Balancing plain text and HTML content helps your emails reach recipients who have HTML images disabled.

39. Stay Away from Email HTML Templates: Plain-text emails perform way better than HTML templates, in terms of inbox deliverability.

For many reasons; such as HTML templates are usually heavy which is not good, those emails take a long time to load especially on mobile, they carry a lot of code behind the scenes which signals to mail providers like Gmail that you're sending promo emails therefore they put you into the promotion tab! 

You can absolutely use a plain-text email while adding some images alongside your logo; it doesn't have to be just text, yet will have a higher chance to find its way to your subscribers' primary inbox.

40. Image/Text Ratio: Having too many images and too little text can make your emails seem spammy. Maintain a healthy balance. This is one of the reasons to do not use HTML templates as well.

41. Link/Text Ratio: Excessive links and too little actual content can raise suspicions. Make sure your emails provide meaningful content, and link text is congruent with the topic of the email.

42. Mobile-Friendly First Emails: Design emails with mobile devices in mind. Most people check emails on their phones, so ensure readability and ease of use.

#5th Pillar: Other factors

43. Easy to Unsubscribe:

Make sure recipients can easily find an unsubscribe option both at the top of your email and at the bottom. This builds trust and reduces the likelihood of your emails being marked as spam (usually happens when they cannot find where the unsubscribe link is). 

I also recommend putting the "manage your subscription" link right next to the "unsubscribe" link to give them a chance to update based on their liking; most of the time they don't want to opt-out completely, but just do not want a specific kind of emails or maybe don't like the frequency, give them an option to choose!

44. Prefer Double Opt-In:

Double opt-in means recipients confirm their subscription twice. It helps ensure you have engaged and willing subscribers, reducing the chances of spam complaints.

45. NO 'No-Reply' Address:

Use a recognizable and monitored reply address. Encourage your subscribers to reply, showing that you're open to communication and improving your sender reputation meanwhile. Most importantly do NOT use “Do not reply” email addresses as they look like “” and this serves as a black hole for incoming mail which you want to avoid.

46. Monitor Your Engagement Metrics:

Track how often your emails are opened, links clicked, and how much revenue your campaigns generate. This data helps refine your strategies for better results.

47. Monitor Your Reputation:

Use tools like the Google Postmaster to monitor your sender reputation and deliverability metrics. This helps you identify and rectify potential issues right on time.

48. Set the Tone with Welcome Email: 

Send a welcome email to new subscribers immediately after they sign up. This sets a positive tone and helps them understand what to expect from your emails. Make sure to keep this first email short!

By following these practices, you can build a strong email marketing foundation that prioritizes recipient preferences, encourages engagement, and improves your overall email deliverability which directly influences your open-rates, and that directly influences the potential revenue you can make out of your list.

And finally, here's some tips for testing your deliverability.

49. Send to a Test Group: Before sending to your entire list, create a small test group consisting of your team members or trusted individuals. Send your email to this group to spot any immediate issues.

50. Check for Deliverability Issues: Monitor if your emails are being delivered successfully or ending up in spam folders. If the latter happens, investigate potential problems.

51. Email Authentication Tests: Perform SPF, DKIM, and DMARC checks using online tools to ensure your authentication setup is correct. Misconfigured authentication can lead to deliverability problems.

52. Test on Different Email Providers: View your email on various email clients (Gmail, Outlook, Yahoo, etc.) and devices (desktop, mobile, tablet). This helps ensure your email displays properly across platforms.

53. Inbox Placement Tests: Use inbox placement testing tools to see where your emails are landing – primary inbox, promotions tab, or spam folder. This helps gauge your deliverability rate.

54. Spam Testing: Run your email content through spam testing tools that analyze your content for potential spam triggers. Adjust your content accordingly if issues are identified.

55. Engagement Tracking: Use your ESP's dahsboard (such as Active Campaign, Klaviyo, etc.) to monitor your engagement metrics such as open rates, click-through rates, and bounce rates. Analyze these metrics to understand how well your emails are performing.

Resources and Tools to Help Test Your Email Deliverability

Mail Tester: This tool lets you check your email's spam score, content, and authentication settings. It provides actionable insights to improve your email deliverability.

Litmus: Litmus offers testing across various email clients and devices, helping you preview how your email will appear to recipients. It also provides spam testing features.

Sender Score: This tool rates the reputation of your sending IP address. A low sender score can affect your email deliverability.

MX Toolbox: MX Toolbox helps you verify your email authentication settings, ensuring that your SPF, DKIM, and DMARC configurations are accurate.

Email on Acid: This tool provides previews of how your email renders on different email clients, enabling you to fix any design issues that may affect deliverability.

Google Postmaster Tools: If you send emails to Gmail addresses, Postmaster Tools offers insights into your sender reputation, delivery errors, and spam complaints.

Engagement Metrics from ESPs: Platforms like Mailchimp, Constant Contact, and others provide detailed engagement metrics to help you assess the success of your email campaigns.

Now it's your turn!

You're fully equipped for ultimate deliverability! Follow the steps in this guide to maximize the deliverability of your emails. Your engagement stats will skyrocket.

If you have any questions, feel free to ask me; either by sending an email to or by scheduling your FREE audit call with me to discover together if you have such deliverability issues at the first place.

If you do, I can lift those filters so you can enjoy increased open rates & maximized revenue by taking full charge of your email list. (:

Talk to you soon,


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