Deliverability Guide

Hey there! You’ve probably noticed sometimes your emails don’t make it to the inbox. Maybe you’ve seen them land in the spam folder and wondered, “What the heck happened?” Well, you’re not alone. I’m not a full-time email deliverability expert, but I’ve been in the trenches for 12 years, sending millions of emails across different countries. I’ve even leaned on professional consultants to make sure things were done right. Now, I’m sharing my experience to help you avoid the mistakes I’ve seen and made and improve your own email deliverability.

Here’s what you’ll get from this guide:

Why Does Deliverability Matter?

Let’s cut to the chase: 1 in 6 legitimate marketing emails doesn’t make it to the inbox. That’s according to Validity’s report. And with an average revenue of $0.10 per email, those lost messages could be costing you a lot.

Imagine sending out 100,000 emails for a campaign—1 in 6 won’t reach its target. That’s a huge hit to your bottom line. So yeah, deliverability matters a lot.

Inbox placement is everything. Even if you think you’re doing well with a 98%+ deliverability rate, your messages might still not be reaching the inbox. Don’t trust those numbers at face value—dig deeper.

Why Email Deliverability Is Tougher Than Ever

We’re not living in 2005 anymore. Email has evolved, and staying on top of the game is harder than ever. Here’s why (Validity):

1. Increased Email Volume: Since COVID-19, global email volumes have doubled. That’s double the competition for inbox space.

2. Apple’s Mail Privacy Protection (MPP): This makes it harder to measure engagement through open rates, which can unintentionally harm deliverability.

3. Tough Economic Conditions: Let’s face it, people are more selective about the emails they open when money is tight.

4. Awareness of Deliverability Issues: More senders are catching on to these challenges, meaning the competition is getting smarter.

Be aware of evolving challenges. With everyone ramping up their email game, it’s not enough to just send messages—you need to send them smart.

How an Email Travels from One Server to Another

Sending an email is a lot like mailing a letter. Picture this: you write a letter, seal it in an envelope, and drop it off at the post office. From there, the post office figures out where your friend lives and routes your letter through a few stops along the way until it reaches the right mailbox.

Simple Mail Transfer Protocol (SMTP) works the same way for emails! When you hit "send," your email is passed off to a server (just like the post office) that knows how to get it to the recipient’s email server. Once it arrives, the email sits in their inbox, waiting for them to open it up and read.

So, in a nutshell, SMTP is the behind-the-scenes process that makes sure your email travels safely from your device to someone else’s inbox—just like the postal service gets your letter from point A to point B.

Now, I won’t dive too deep into the technical stuff, but the illustration shows a simplified version of what happens between the sending mail server and the receiving mail server.

When Things Go Wrong

Of course, things can break along the way. If something goes wrong, you’ll get an SMTP error code, which lets you know whether it’s a temporary issue or a bigger problem. If you’re not sure where to find these error codes in your email service provider (ESP), don’t hesitate to reach out to their support team for help.

Bounced Emails: Why They Happen

You’re probably thinking, “Wait a second, is this where the bounces come into play?” Yep, you’ve nailed it! This is exactly when bounces happen, and they come in a few different flavors.

🟡 Soft bounces (4xx error codes)
These are the “not right now” kind of bounces. Soft bounces happen when there’s a temporary problem delivering your email. Maybe the recipient’s inbox is full, or the email server is down for a bit. The good news? The email server will usually try again later. The bad news? The message hasn’t been delivered yet, so it's hanging out in limbo for now.

🛑 Hard bounces (5xx error codes)
Hard bounces are a more permanent issue. They happen when an email is completely rejected because of something like an invalid email address, a non-existent domain, or just a plain wrong email. These emails aren’t going anywhere unless you fix the issue—there’s no second chance here.

🚫 Block bounces (550 error code)
This is when the recipient's email server slams the door in your face. It happens when your email gets rejected outright, often because of security reasons. Maybe your sender’s domain has been blacklisted, flagged as spam, or outright blocked. No matter the reason, the email won’t even make it past the front door.

Bounces—whether soft, hard, or block—only scratch the surface of what can go wrong in the email delivery process. SMTP error codes are the server’s way of giving you a status update on what went wrong, and they cover a lot more than just bounces. If you want to geek out over the full list of error codes, you can check them out here.

The Inbox Journey: Key Checks Before Your Email Arrives

So, we’ve covered how your email is sent, but before it lands in someone’s inbox, it has to pass through a series of important checks. Think of it like your email going through a quality control process—it needs to meet certain criteria to be delivered successfully.

Here are the five key checks every email faces:

1️⃣ Authentication
This is your email’s ID card. Without proper SPF, DKIM, and DMARC setup, email providers can’t confirm that the message is really from you, and that’s a big red flag. It’s the first line of defense for inboxes.

2️⃣ Reputation Check
Just like a reputation in real life, if your email sender reputation isn’t good, you’re going to run into trouble. If you’ve had a history of sending unwanted emails, or if people aren’t engaging with your content, your reputation takes a hit, and your deliverability will too.

3️⃣ Content Filtering
Email providers are like bouncers at a club—they’re checking to make sure your email doesn’t look suspicious. If your email has too many spammy words, all-caps, or excessive links, it could get flagged as junk before it even has a chance to make an impression.

4️⃣ User Engagement Metrics
How people interact with your emails makes a huge difference. Are they opening them, clicking links, or just ignoring them? Low engagement sends a message to email providers that your emails aren’t wanted, and that can affect future deliveries.

5️⃣ Inbox Placement Decision
This is the final checkpoint. After passing through all the filters, your email is either rewarded with a spot in the primary inbox or sent off to less desirable tabs like promotions or, worse, spam. All the previous checks lead up to this moment.

Let’s break these down further so you can make sure your emails are passing every check with flying colors.

1️⃣ Authentication: Making Sure Your Emails Are Legit

Back in the early 2000s, email systems were a bit like the wild west—anyone could pretend to be someone else. This led to a huge surge in email fraud and spam. People were sending fake emails left and right, tricking others into giving up sensitive info (this is where phishing attacks took off). So, email authentication was born to solve that problem.

Authentication helps ensure that emails really come from who they say they do, instead of someone pretending to be you.

Let’s break down the key players in this process:

〰️ SPF (Sender Policy Framework)
Think of SPF like a guest list. It checks if the email address sending the message is allowed to send emails on behalf of your domain. You basically tell the email system, “These are the addresses that are cool to send emails from my domain.” If an email comes from an unauthorized address, it’s going to get rejected.

〰️ DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your email, like a stamp of approval that proves the email hasn’t been tampered with. It tells the recipient's server, “This email is legit and hasn’t been altered on its journey.”

〰️ DMARC (Domain-based Message Authentication, Reporting & Conformance) DMARC is like the referee—it enforces the rules. It uses both SPF and DKIM to decide whether an email should be delivered or blocked. Plus, it gives you reports on how your emails are doing, so you know if something's going wrong.

〰️ BIMI (Brand Indicators for Message Identification)
This is the fancy touch. BIMI allows your brand’s logo to show up next to your emails in the inbox—think of it like your brand’s badge of authenticity. But here’s the catch: BIMI only works if you’ve set up DMARC properly. It’s a nice way to build trust with your recipients and stand out in the inbox.

It’s all about making sure your emails are trustworthy and secure, so your recipients feel confident opening them.

How Can I Check My Authentication Setup?

At this point, you might be thinking, “Okay, but how do I know if my setup is good?” Well, let me introduce you to aboutmy.email. This tool will give you a health check of your email deliverability setup. It’s pretty cool because it pulls everything into one place and gives you all the nerdy details—though we won’t dive into all of that here.

Here’s what you need to do:

1. Head to aboutmy.email and generate a special email.

2. Send your newsletter to that email.

3. Wait for the results to pop up. You’ll get a summary of different checks and results, plus a sidebar with more categories to explore.

How Can I Improve my Authentication?

If your reports show error messages, don’t panic. There are plenty of free tools, like easydmarc, that can help you fix them. They’ll explain the different elements and guide you through what needs to be done.

I remember when I did my first email migration, and let me tell you, those abbreviations (SPF, DKIM, DMARC) were like a foreign language! But don’t worry—the tools will help you figure it out bit by bit.

Once your records are good to go, you’ll need to implement them. This means finding whoever manages your domain (for me, it’s GoDaddy, where I bought insidecrm.io). It’s usually a quick fix—about a minute job—but if tech puts you at the bottom of the list, maybe bribe them with a little chocolate to speed things up.

A Little Story on BIMI

I remember the old days when you needed a Google+ account just to see your logo in the Gmail inbox. It was a hassle, but hey, at least it was free. Fast forward to today, and now you’ve got to pay around $1,000 a year just to display your logo with BIMI. Not exactly a bargain.

I did some research, and honestly, I couldn’t find a solid study that proves BIMI makes a significant impact. You can’t really A/B test it either. Sure, you can insert the logo without the extra certifications, but no one’s really sure how much visibility that gets you. If you want to dig into whether it’s worth the investment, check out this great article over at All About Email.

2️⃣ My Reputation is Everything

Your sender reputation is like your email’s street cred—it’s how email service providers (ESPs) decide whether to trust your messages or toss them into the spam folder. Think of it as your email's "credit score." A good score opens doors, while a bad one slams them shut.

Your reputation is built on two main pillars: IP reputation and domain reputation. Let’s break it down:

🔢 IP Reputation
Every email you send out comes from an IP address. It might look something like this: 192.168.123.132. Your ESP assigns this to you, and it could be shared with other senders (shared IP) or exclusively yours (dedicated IP). This is the “home address” the server checks to determine if you’re a trustworthy sender.

Here’s the catch: it’s super easy to damage your IP reputation with just a few bad emails, but fixing it can take weeks or even months. So, protect it like gold!

🏡 Domain Reputation
Your domain, like mine—insidecrm.io—also needs to have a good reputation. The reason? You can swap out IPs and get fresh ones, but your domain stays tied to your sending behaviour. If your domain starts to look shady, you’ll have a tough time getting into inboxes, no matter how many new IPs you buy.

What Factors Impact My Reputation?

Here’s what can make or break your sender reputation:

〰️ Spam Complaints
When people click “Report as Spam,” it’s like dinging your credit score. The more complaints, the worse your reputation gets. Keep that number low to stay in good standing.

〰️ Spam Traps
These are sneaky email addresses set up by ISPs to catch spammers. They look like normal email accounts, but if you send to one, your domain could get blacklisted fast.

〰️ Bounce Rates
Bounces happen when emails don’t make it to their destination. Soft bounces are temporary (think full inboxes), but hard bounces are permanent (bad or non-existent email addresses). Too many of either, and your reputation takes a hit.

〰️ Engagement
This is all about how people interact with your emails—do they open, click, or reply? Strong engagement shows ISPs that your emails are wanted, which helps your reputation.

〰️ Sending Volume and Consistency
Sending too many emails too fast or having irregular sending patterns can raise red flags with ISPs. Consistency is key—build trust over time, don’t go overboard in one go.

〰️ Unsubscribe Rates
While not as damaging as spam complaints, high unsubscribe rates are still a warning sign. If lots of people are jumping ship, ISPs might take notice.

The Unsubscribe Dilemma

Let’s talk about unsubscribes for a second. A lot of email marketers make it hard for users to unsubscribe, thinking it’ll keep people on their list. But honestly? That’s a quick way to tank your sender reputation.

Here’s why: if someone doesn’t want your emails anymore, they’re going to find a way out. If they can’t easily unsubscribe, they might mark your emails as spam, or worse, just stop engaging altogether. Both of these actions hurt your reputation.

Google Postmaster: Your Reputation HQ

If you’re serious about keeping tabs on your sender reputation, you need to know about Google Postmaster. Since Gmail is one of the most popular inbox providers (about 50% of email addresses at many companies are Gmail accounts), it’s a good idea to monitor your reputation specifically with Google.

Google Postmaster is a free tool that lets you see your reputation with Google domains (like @gmail.com). It shows you data on authentication, spam rate, and unsubscribe behavior, so you can spot issues before they spiral out of control.

Here’s what you can expect:

• Compliance status: A checklist that tells you if your emails are meeting Google’s standards based on factors like authentication and spam rate.

• Spam rate: Shows how many of your emails are marked as spam.

For the nerds out there, you can dive deeper by visiting the “Old Postmaster Tools” section, where you can check your IP and domain reputation. The setup is simple, but it takes a few days for the data to start showing up, so don’t worry if it doesn’t appear right away. You might not need to check this every day, but it’s a lifesaver when your performance dips unexpectedly, and you need answers fast.

3️⃣ Content Essentials: Craft Emails That Land in the Inbox

Can I tell you exactly which content elements will determine whether your email lands in the inbox or the spam folder? Not 100%. But I’ve got a solid checklist of best practices that can give you a real edge. These tips will help improve your chances.

Here’s what you should keep in mind:

✅ Subject Line and Preheader Length
Keep your subject lines and preheaders within recommended character limits. Too long, and they’ll get cut off—especially on mobile. Make sure your message is clear and compelling in the space you have.

✅ Avoid Spammy Language
Certain words are like red flags to spam filters. Words like “FREE,” “WIN,” and using all caps can trigger those filters, sending your email straight to spam. Keep it conversational and professional.

✅ Keep Links Consistent
Make sure all your links come from the same domain. If your email contains links from multiple domains, it can raise suspicions and affect deliverability.

✅ Use Alt Text for Images
Every image in your email should have descriptive alt text. This not only helps with accessibility but also ensures that your message still gets across if images don’t load.

✅ Balance Image-to-Text Ratio
A big no-no is sending image-heavy emails with hardly any text. Keep a balance—too many images and not enough text can get your email flagged by spam filters.

✅ Watch Your Email Size
Keep your email under 102 KB. Why? Because Gmail cuts off emails that are too big, forcing users to click a “View Entire Message” link. That’s an extra step for your readers that you want to avoid.

✅ Design for All Devices
Your email needs to look great on every device, whether it’s a desktop or a phone. Following mobile-friendly best practices ensures your email gets read, not deleted.

✅ Keep Width in Check
Stick to a maximum width of 600px for desktop and 320px for mobile. Wider than that, and your email could end up looking wonky on different devices.

✅ Clean HTML Code
Messy or broken HTML can break your email layout, make it unresponsive, and even get flagged by spam filters. Double-check your code and keep it clean.

✅ Easy Unsubscribe
Make unsubscribing simple. Don’t hide the unsubscribe link. A difficult unsubscribe process can lead to spam complaints, which hurt your reputation and deliverability.

Following these best practices gives you a better shot at getting your email delivered and read. Sure, inbox placement is a complex game, but taking these steps gets you closer to winning it.

4️⃣ Engagement Rules: How Your Audience Impacts Your Email Reputation

When it comes to email marketing, engagement metrics are like your report card. They tell the world (and the ISPs) how your emails are performing. If your engagement is high, it’s a green light for your sender reputation. If it’s low? Well, that’s when deliverability can start to take a hit.

Let’s break it down into positive and negative engagement metrics, and how each one impacts your reputation.

🚀 Positive Engagement Metrics

➕ Open Rates
A high open rate shows that people actually want to read your emails. It’s like telling ISPs, “Hey, these emails are valued,” and that gives your sender reputation a solid boost.

➕ Click-Through Rates (CTR)
It’s great if people are opening your emails, but even better if they’re clicking through to your content. A strong CTR means your emails are not just getting opened—they’re engaging, which reflects positively on your reputation.

➕ Reply Rates
When recipients hit reply, it’s a big win. This kind of interaction shows that your emails are personal and valuable. Pro tip: Use a real, personalised “Reply-To” address to encourage more responses.

➕ Forwarding
If people are forwarding your emails, that’s gold. It’s a major signal to ISPs that your content is worth sharing, and that can only help your reputation.

➕ Time Spent Reading
The longer people spend reading your emails, the better. ISPs factor in how much time recipients are engaging with your content, so aim to create emails that hold attention.

🚨Negative Engagement Metrics

➖ Spam Complaints
If recipients are marking your emails as spam, that’s a major red flag. It’s like telling ISPs, “This email is unwanted,” and that can do serious damage to your reputation.

➖ Bounce Rates
A high bounce rate—especially hard bounces (invalid email addresses)—hurts your sender reputation. It signals that your email list might be outdated or full of inactive addresses.

➖ Low Engagement Rates
If your open rates and click-through rates are consistently low, ISPs start to get the hint that your emails aren’t resonating with your audience. This can negatively impact your deliverability over time.

➖ Deletion Without Reading
If recipients are constantly deleting your emails without opening them, it’s a bad sign. ISPs will take this as a signal that your content isn’t relevant, which can hurt your chances of getting into the inbox in the future.

5️⃣ Inbox Placement: Getting Into the Right Tab

Back in 2013, Gmail shook up the email world by introducing the Promotions tab. Marketers everywhere panicked, wondering if their emails would ever be seen again. And here we are, still asking, "Did I land in the inbox, or am I stuck in Promotions?"

Now, Gmail doesn’t reveal the full details behind its sorting algorithm, but we do know that it uses the content of your email and the sender address to decide where to place incoming messages.

Here’s a quick breakdown of Gmail’s inbox tabs:

• Primary tab: This is where the magic happens. It’s for personal emails and important notifications—basically, the emails people pay the most attention to.

• Social tab: For messages from social media platforms like Facebook, Twitter, and Instagram.

• Updates tab: Here’s where transactional emails like shipping notifications or changes to shared Google Docs land.

• Forums tab: This one’s for emails from discussion groups, forums, or mailing lists.

Why the Primary Tab Matters

When we talk about inbox placement, we’re really talking about landing in the Primary tab. That’s where you want to be. According to a survey by Zerobounce, 25% of people never check their Promotions tab. And as for the spam folder? Forget it—27% check it just a few times a year, and 15% never check it at all.

Here’s the thing: delivery rate (whether the email was accepted by the server) doesn’t tell you where it landed. For that, you need to track your inbox placement.

Tools for Inbox Placement

If you’re serious about figuring out where your emails are ending up, tools like Evernest (formerly 250OK) can help. They provide a seed list of email addresses for you to send emails to. These addresses report back whether the emails landed in the inbox, Promotions, or somewhere else. You can track this data on a dashboard to get an idea of your inbox placement rate.

But a word of advice: this step is really more useful for larger senders. There’s plenty you can improve on before you need to dive this deep.

What I Didn’t Cover

There’s a lot more to unpack when it comes to email deliverability. But for now, I’ve focused on understanding the basics and some quick fixes. Here are a few topics I didn’t touch (or only briefly mentioned):

• List hygiene & segmentation

• IP warming

• Spam traps

• Sending history

• Double opt-in best practices

• Unsubscribe management

• Blacklisting

• How to handle high bounce rates

• Feedback loops

If you like to see a Guide 2.0 covering these topics, leave a comment on LinkedIn.

Key Takeaways from the Guide

Now that we’ve covered the essentials, here are the key takeaways from everything we’ve talked about:

1. Deliverability matters: Landing in the inbox (especially the Primary tab) is crucial. Even a high delivery rate doesn’t guarantee visibility.

2. Reputation is everything: Your sender reputation, whether tied to your IP or domain, is the biggest factor in whether your emails make it to the inbox. Keep it strong by avoiding spam complaints and bounces, and by maintaining engagement.

3. Authentication is a must: Setting up SPF, DKIM, and DMARC ensures your emails are trusted by email providers. Without proper authentication, your emails might never make it past the gate.

4. Content matters: Use best practices like avoiding spammy language, keeping your subject lines concise, and balancing image-to-text ratios to improve your chances of landing in the inbox.

5. Engagement is key: Positive engagement metrics like high open rates and click-throughs boost your sender reputation, while negative metrics (spam complaints, high bounce rates) can hurt your deliverability.

6. Inbox placement tools: For larger senders, tools like Evernest can help track exactly where your emails are landing, but make sure you’ve mastered the basics before diving into this level of detail.