What is Email Deliverability? Tips and Best Practices

Email deliverability is the ability to get your emails delivered to the inbox of your subscribers (not the spam folder). In other words, it’s about making sure your carefully written marketing emails actually reach your audience’s main inbox and avoid getting blocked or filtered out. You might spend hours writing great copy and designing beautiful templates, but if your emails don’t land in inboxes, your audience will never even see them.

In this article, you’ll learn what email deliverability is, why it matters to you, the factors that affect it, and practical tips to improve it. We’ll also cover how building an engaged email list using tools like Poptin can boost your deliverability in the long run.

Understanding Email Deliverability (and Why It Matters)

Email deliverability refers to whether your email successfully arrives in a subscriber’s inbox without bouncing or getting marked as spam. It’s often measured as an “inbox placement rate” – the percentage of sent emails that avoid spam filters and show up where they’re supposed to. Don’t confuse this with email delivery, which simply means the email was accepted by the recipient’s mail server (it could still land in spam). Deliverability goes a step further: it’s about getting into the inbox where your subscriber will actually see and (hopefully) read your message.

Why does email deliverability matter? 

If your emails don’t reach people, nothing else you do matters. Every conversion from email starts with a delivered message. High deliverability ensures your campaigns can achieve their goals:

• Reaching your audience: Subscribers can only open and act on emails if they land in the inbox. If emails go to spam, they are likely never seen. High deliverability ensures your message reaches the right people..
• Maximizing ROI: Email marketing delivers up to $36 for every $1 spent. That ROI depends on emails actually reaching inboxes. Poor deliverability means lost revenue and wasted marketing spend. Ensuring good deliverability maximizes visibility and engagement.
• Building trust and reputation: Inbox placement builds credibility with subscribers and mailbox providers. Recognized emails increase brand trust and engagement. Gmail, Yahoo, and others track sender behavior over time. A strong sender reputation improves future inbox placement.
• Protecting your brand: Poor deliverability can get emails flagged as spam. Spam complaints hurt campaign performance and brand reputation. Mailbox providers may penalize your domain for frequent spam reports. Good deliverability safeguards your brand and sender reputation.
  
  Example: Even if you have a 98% delivery rate (meaning 98% of your emails aren’t bounced by servers), that remaining 2% of undelivered emails can be significant. For a send to 1,000 subscribers, 20 people would never see your message . And if some delivered emails quietly land in spam, your real audience reach shrinks further. This illustrates why focusing on deliverability is so important – it directly impacts how many subscribers actually lay eyes on your content. In short, better deliverability = more opens, clicks, and conversions.

Read more: From Spam Folder to Inbox Hero: Email Deliverability for Niche Industries

Factors That Affect Email Deliverability

Several factors determine whether your emails make it to the inbox. Understanding these factors will help you pinpoint what to improve. The key aspects include your sender reputation, authentication, list quality, subscriber engagement, email content, and sending behavior. Let’s break down each:

• Sender Reputation: This is essentially your email sender “score” or credibility in the eyes of inbox providers. ISPs (Internet Service Providers) and mailbox providers assign senders a reputation score (often 0–100) based on how recipients interact with your emails. If many people frequently delete your emails, mark them as spam, or if you have high bounce rates, your score will drop. A low sender score tells providers that users don’t trust or want your emails, leading to more of your messages being filtered out . On the other hand, a good track record (low complaints, low bounces, solid engagement) improves your reputation, making providers more confident in delivering your mail. Out of all deliverability factors, sender reputation is one of the most important, because it’s like your email “credit score” – it affects everything else.
  
• Email Authentication & Infrastructure: Proper technical setup of your sending domain and servers is critical. Email authentication protocols – SPF, DKIM, and DMARC – validate that your emails are really sent by you (and not forged by spammers). If you haven’t set these up, your emails are more likely to be doubted or blocked by mail servers. In fact, having SPF, DKIM, and DMARC in place has gone from a nice-to-have to a must-have for any legitimate email program. These protocols work together to prove your messages aren’t spoofed, which builds trust with mailbox providers and improves deliverability. Additionally, your sending infrastructure – like whether you use a shared or dedicated IP address – matters. Large senders often use a dedicated IP to control their reputation. If you suddenly send a huge volume of email from a new IP or domain, that can look suspicious (more on send volume later). In short, authentication and a stable infrastructure signal to ISPs that you are a legitimate sender, not a spammer.
  
• Email Content & Design: What you include in your emails can trigger spam filters. Providers scan email content for red flags. Things like excessive use of ALL CAPS, a lot of spam trigger words (“Free money!!!”), or deceptive subject lines can hurt deliverability. For instance, using all caps in subject lines can lower response rates significantly and come across as “shouting” or spammy. Your email’s formatting matters too: a message that is one giant image with little text, or includes certain types of attachments or scripts, might be blocked. The goal is to create emails that look legitimate and relevant: clear subject lines, a healthy balance of text to images, and no weird code. Engaging, valuable content also keeps readers interested, which helps with the next factor (engagement).
  
• Subscriber Engagement: Email providers increasingly use engagement signals to decide deliverability. If recipients consistently open, read, reply to, or click your emails, it’s a positive sign that your emails are wanted. Positive engagement signals (opens, clicks) build your credibility and improve inbox placement for future sends . Conversely, if many users ignore your emails, delete them without reading, or mark them as spam, that’s a negative signal. Think of it this way: providers like Gmail or Outlook are watching how their users react to your messages. Lots of engagement = “this sender provides value, we’ll keep delivering to inbox.” Lots of deletions or spam flags = “users don’t like this, better send it to spam.” Thus, senders with higher engagement rates tend to enjoy better deliverability. This is why sending relevant content to the right people (and pruning those who never engage) is so important for keeping you in the inbox.
  
• Email List Quality (Hygiene): The quality of your email list has a direct impact on deliverability. A “clean” list is one that contains valid, opted-in, and active email addresses. If your list has a lot of invalid addresses (hard bounces) or spam traps, or people who never gave permission, you’ll get high bounce rates and spam complaints – both of which wreck deliverability. Internet providers see high bounce rates as a sign of a poor sender (you’re not maintaining your list). Spam complaints obviously hurt your reputation. Good list hygiene means you regularly remove or correct bad addresses, avoid sending to people who never engage, and never use purchased lists. For example, repeatedly emailing addresses that hard-bounce can aggravate the bounce rate and raise red flags with ISPs . On the flip side, senders who prioritize list hygiene see big benefits. 
  
• Sending Frequency & Volume: How you send emails (how often and how many) also affects deliverability. Sudden spikes in email volume or irregular sending patterns can look like spam activity. ISPs notice if you go from sending 1,000 emails a week to 100,000 in a day – it’s a red flag for possible spam. Likewise, if you blast a huge list very infrequently (say, once a year), many recipients might not remember you and mark you as spam when that one email arrives. It’s better to have a steady, consistent sending schedule that keeps your audience familiar with your emails. If you need to increase volume (e.g., your list is growing or you have a big campaign), it’s wise to “warm up” your sending IP/domain by gradually raising the volume so you can build a positive reputation as you scale. Think of it like not overwhelming the postal system all at once. Regular, periodic sending also keeps your subscribers engaged over time, rather than surprising them out of the blue after long silences .

Each of these factors is in your control to some degree, which is good news. You can adjust your practices to improve each area. For example, if you find your emails often go to spam, you might investigate: Is my sender reputation low? (Maybe due to an old, unengaged list.) Am I missing SPF/DKIM authentication? Does my content look spammy? Below, we’ll cover best practices to tackle these areas and boost your deliverability.

Best Practices to Improve Email Deliverability

Improving email deliverability is about adopting good sending habits, proper technical setups, and subscriber-friendly tactics. Here are some proven best practices you should follow:

1. Implement Email Authentication (SPF, DKIM, DMARC)

One of the first things you should do is set up the standard email authentication methods for your sending domain: SPF, DKIM, and DMARC. These might sound technical, but they are essentially tools that prove to mailbox providers that you are who you claim to be as a sender. Enabling them is crucial for deliverability – many mail providers will divert or reject emails that aren’t authenticated because they could be phishing or spam.

• SPF (Sender Policy Framework): SPF allows you to specify which mail servers are allowed to send email on behalf of your domain. You do this by adding an SPF record in your domain’s DNS. When an email arrives claiming to be from your domain, the receiving server checks that DNS record to see if the sending server’s IP is listed. If it is, the email passes SPF. This prevents spammers from forging your domain in their emails. 
  
  How it helps deliverability: By publishing an SPF record, you’re telling the world “these servers are legit senders for my domain.” It reduces the chance of your domain being used for spoofing, which means receivers trust your mail more. (Unauthorized servers will fail SPF, and those fake emails can be filtered out, protecting your brand.) Simply put, SPF is a foundational layer of trust – and one of the “must-follow” protocols for good deliverability.
  
• DKIM (DomainKeys Identified Mail): DKIM adds a digital signature to each email you send, which recipients can verify to ensure the message wasn’t altered and truly comes from your domain. You generate a pair of cryptographic keys (one private, one public). Your sending mail server uses the private key to sign the header of each outgoing email. Recipients use your public key (published via DNS) to verify that the signature is valid. If the signature checks out, it confirms the email’s content wasn’t tampered with and it was authorized by your domain. 
  
  How it helps deliverability: Like SPF, DKIM builds trust. It’s essentially a certificate of authenticity for your emails. Valid DKIM signatures show that the email is legit and hasn’t been forged mid-transit.
  
• DMARC (Domain-based Message Authentication, Reporting & Conformance): DMARC ties together SPF and DKIM and adds an extra policy layer. With DMARC, you publish a policy telling receivers what to do if an email fails SPF/DKIM checks (e.g., quarantine it or reject it). It also provides a reporting mechanism so you can get feedback on who’s sending emails purporting to be from your domain. Essentially, DMARC says “If an email isn’t authenticated by SPF and/or DKIM, and it’s not aligning with my domain, then take X action (like send it to spam).” 
  
  How it helps deliverability: DMARC prevents spammers from misusing your domain by specifying that unauthenticated mail should be discarded or flagged. This protects your brand from phishing and ensures that only properly authenticated emails make it to inboxes. Moreover, mailbox providers increasingly require DMARC for sending domains because it’s a sign of a responsible sender. By implementing DMARC (with a policy to reject or quarantine failures), you show ISPs that you’re serious about email integrity, which can positively impact your reputation. Plus, the DMARC reports you receive help to monitor your authentication status and spot any abuse of your domain. Overall, SPF, DKIM, and DMARC work in tandem to legitimize your emails, and today they are foundational for good deliverability.
  
  To get these set up, you might need help from your IT team or your email service provider’s documentation – but it’s usually a one-time configuration in your DNS and email platform. Once in place, you’ll immediately benefit. Many email marketing platforms will show you if you have these records missing; make it a priority to fix that. Remember, authenticated emails have a much better chance of landing in the inbox, because providers can trust their origin 

2. Maintain a Clean, Permission-Based Email List (List Hygiene)

Another top deliverability booster is keeping your email list healthy. This starts from how you build your list and continues with how you maintain it over time. Here are key practices:

• Use confirmed opt-in (double opt-in) when possible: This means when someone signs up for your emails, you send a confirmation email asking them to click a link to verify. Confirmed opt-in ensures the address is valid and that the person really wants to subscribe (they took an extra step). This prevents typos and fake sign-ups from polluting your list. It also immediately engages the new subscriber – a welcome message right after signup gets them used to seeing your emails.
  
• Never buy or scrape email lists: It might be tempting to quickly grow your reach by purchasing a list of “targeted” emails or scraping contacts off the web, but this is extremely risky and usually counterproductive. Purchased lists often contain people who never agreed to hear from you – so your emails to them are unsolicited (ripe for spam complaints). They may also contain spam trap addresses or a high volume of invalids, which will torpedo your sender reputation. Most email service providers forbid using bought lists, and for good reason. Stick to organic list growth methods and email people who actually gave you permission. Sending to folks who didn’t opt in is one of the quickest ways to get blacklisted or filtered.
  
• Regularly clean your list: Over time, even a legitimately built list will accumulate some bad addresses or unengaged users. It’s important to periodically remove or attempt to re-engage inactive subscribers. If someone hasn’t opened or clicked any of your emails in, say, 6-12 months, it may be worth sending a re-engagement email (“Do you still want to hear from us?”) and if they remain unresponsive, consider stopping email to them. Why? Because continuing to send to a large cohort of unengaged recipients can hurt your deliverability – it lowers your open rates (a negative signal) and those addresses could turn into spam traps. Similarly, always remove hard bounces (invalid emails) immediately, and monitor for repeated soft bounces. Keeping bounces low is critical; ISPs use bounce rates to gauge your list quality.
  
• Honor unsubscribes and complaints promptly: Make sure you have a clear unsubscribe link in every email (required by law in many cases), and if someone opts out, remove them from your list quickly. Never try to hide the unsubscribe link or make it hard to find – that’ll just cause frustrated users to mark your message as spam, which is far worse. Also, many mailbox providers offer “feedback loops” where if a user marks your email as spam, you can get notified. If you have access to those (often through your ESP), use them to ensure you don’t keep mailing those who complained. Being proactive about this helps keep your complaint rate low and shows ISPs you’re a responsible sender.
  
• Segment and target your emails: This is more of a marketing practice, but it has deliverability implications. If you segment your list (for example, by interest, purchase history, etc.), you can send more relevant content to each group. That typically leads to higher engagement (people are getting content they care about), which in turn boosts deliverability. It can also prevent you from over-mailing certain subscribers. For instance, you might send daily emails to your most active customers, but only weekly to others. By tailoring frequency and content, you keep engagement up and complaints down. Better engagement = better reputation = better deliverability, as we noted.
  

3. Optimize Your Email Content and Design

The content of your emails – both the wording and the design/formatting – can influence whether they pass spam filters and engage readers. Here are best practices to ensure your content isn’t hurting deliverability:

• Write clear, non-spammy subject lines: Your subject line is the first thing both the user and spam filters see. Avoid gimmicky tactics: don’t use ALL CAPS, avoid excessive punctuation (e.g., “!!!”), and be cautious with words that are common in spam. Words like “Free $$$”, “Act Now”, “Guaranteed winner”, etc., can trigger filters if overused. That doesn’t mean you can never say “free” – just use marketing language thoughtfully and sparingly.
  Make the subject line relevant to the content and the audience. A good rule of thumb from experts: if it sounds like something a sketchy used-car salesperson would say, it’s probably a spam trigger Instead, focus on clarity and value – e.g. “Exclusive 20% Discount for Your Next Order” is better than “!!!EXCLUSIVE FREE OFFER CLICK NOW!!!”. Also, keep it reasonably short and to the point. 
  
• Avoid certain red flag elements: There are a few content elements that are known no-nos for deliverability:
  
  • Large image-only emails: Emails that are one big image (with little or no text) are often spammy. Always include proper text content – not just images – because filters can’t read images and thus treat image-only emails with suspicion.
  • Attachments in marketing emails: Attaching files (PDFs, Word docs, etc.) in bulk emails is usually discouraged. Attachments can carry viruses, so many mail systems block them or flag the email. Instead of an attachment, host the file on your website and link to it. 
  • Embedded media or scripts: Don’t try to embed video players, Flash, or complicated JavaScript in an email. Most email clients will strip these out or break them, and just attempting to include them might set off filters. A safer approach is to include a thumbnail image with a play button that links to a video on your site, rather than embedding a video. Similarly, use simple HTML and inline CSS; avoid forms or fancy interactive scripts inside emails (they likely won’t work and could look suspect).
    
• Optimize the text-to-image ratio: A common best practice is to have a good balance of text and images. All-text emails can look plain (and all-image is bad as mentioned), so mix them. Provide meaningful text that describes the images (including ALT text on images). Many spam filters like to see at least some text. Also, some users have images off by default, so an email should still convey something with images disabled.
  
• Include required info and a clear footer: Legitimate marketing emails should include your physical mailing address (per anti-spam laws like CAN-SPAM) and an unsubscribe link. Failing to include these can trigger compliance filters. Plus, a visible unsubscribe link is actually good for deliverability – it gives unhappy recipients a way to opt-out rather than hitting the spam button. Make sure the sender (“From”) email is a valid address that can receive replies (no-reply@ addresses are not very user-friendly; consider using an alias that can at least auto-respond or be monitored).
  
• Personalize and add value: While not a direct technical filter issue, making your content relevant and valuable to the reader will naturally improve engagement. For example, using the subscriber’s name or referencing their recent activity in the email can catch their attention. If your content consistently provides something the subscriber cares about (be it discounts, useful tips, or important updates), they’re more likely to open and interact, which feeds positive engagement signals back to mailbox providers. Engaged readers are also less likely to report you as spam. So, good content is a win-win: it drives your marketing goals and keeps your deliverability strong.
  
• Test your emails before sending: Many tools (like Litmus, Email on Acid, or even your ESP’s built-in checker) can test your email for spam triggers or rendering issues. They’ll flag things like broken links, missing ALT text, or words that might trigger filters. It’s wise to test especially important campaigns. These tools can also show you how your email looks in different email clients – ensuring a consistent, professional appearance everywhere.
  

4. Send Emails Consistently and Monitor Your Sending Frequency

As mentioned earlier in the factors, how you send can impact deliverability. Establishing a consistent sending schedule builds a rhythm with both your subscribers and ISPs:

• Set expectations and meet them: When someone signs up for your emails, ideally they should know roughly how often they’ll hear from you. Whether it’s a weekly newsletter or occasional product updates, try to stick to a consistent cadence. If you send too infrequently, people may forget who you are and report the next email as spam out of confusion. If you send too often, you risk annoying subscribers and prompting them to unsubscribe or mark spam. There’s no one-size frequency that fits all – it depends on your content and audience – but make sure whatever you choose is sustainable and in line with what you promised. For instance, if users signed up for a “monthly digest,” don’t suddenly start emailing them every day.
  
• Gradually warm up new IPs or domains: If you are starting to send from a new email domain or a new dedicated IP address (for example, you moved to a new email service or you’re separating your mail streams), don’t send your whole volume at once. ISPs are wary of new senders blasting high volumes (could be a spammer jumping IPs). Instead, warm up the IP/domain by sending smaller volumes at first and ramping up over days or weeks. This lets you build a positive reputation incrementally. During warming, send to your most engaged subscribers first – their opens and clicks will signal good engagement to ISPs. Many ESPs provide guidelines or automated warm-up schedules to help with this. The key is patience: a stable build-up will pay off in higher inbox placement as you scale, whereas a sudden flood might get throttled or spam-filtered
  
• Watch out for spikes in volume: Even if you have an established sending history, be cautious with sudden large campaigns. For example, an e-commerce site that usually sends 2 emails a week might decide to send 5 different emails during Black Friday week. That spike, especially if to your full list each time, could impact deliverability. It’s not to say you can’t send more during special periods – just monitor it. Sometimes splitting the send over a few days or segmenting the audience can mitigate issues. Also, ensure that big sends are really targeted and necessary; don’t send to your whole database if only a segment is relevant.
  
• Monitor engagement and adjust frequency if needed: Keep an eye on open rates, click rates, and unsubscribe/spam rates as you adjust frequency. If you notice open rates dropping and unsubscribes rising when you increase sends, that’s a sign you may be over-mailing. On the other hand, if you email very infrequently and see poor engagement, the list might be going cold – you may need to either send a bit more often or at least reintroduce yourself when you do send. It’s a fine balance that you can calibrate by watching these metrics.
  
• Send at optimal times if possible: While not a core deliverability factor, sending when subscribers are likely to check email can maximize engagement (which indirectly benefits deliverability). Research into best send times can guide you (for example, some studies find mid-morning or mid-week often perform well) Most importantly, avoid sending in the middle of the night or other odd hours if your audience is local – you don’t want your emails to always be buried under a pile of newer morning emails when the user wakes up.
  

Read more: What’s the Best Time to Send Marketing Emails?

5. Monitor Your Sender Reputation and Deliverability Metrics

Improving deliverability isn’t a one-and-done task – it requires ongoing monitoring. Keep an eye on key metrics that reflect your deliverability:

• Bounce rate: This tells you the percentage of emails that weren’t delivered (bounced back). A high bounce rate (especially high hard bounces for nonexistent addresses) is a warning sign. If you see this rising, pause and investigate – maybe a list got stale or you had a list collection that wasn’t validated. Consistently high bounce rates will degrade your reputation so you want this number as low as possible (generally under 2% for hard bounces is a common benchmark, though lower is better).
  
• Spam complaint rate: Most ESPs will show you how many recipients marked your email as spam (if you’re integrated with feedback loops). This percentage should be extremely low (well under 0.1% per campaign ideally). If you ever see a spike, analyze that send: Were you mailing older addresses? Did the content or subject trigger people negatively? Even a small number of complaints is very damaging, so always work to minimize this by following the best practices above (permission-based list, easy opt-out, relevant content).
  
• Open and click rates: While open rates are becoming trickier to measure accurately (due to privacy changes), they still give a directional idea of engagement. A declining open rate over time could mean more emails are going to spam or being ignored. High open and click rates are a sign of a healthy email program and also indicate good deliverability (emails in inbox tend to get opened more). Positive engagement like opens/clicks “improves your chances of inbox placement for future sends” . If you use tools that measure inbox placement directly (some services can tell you what percentage of emails went to inbox vs spam for seed accounts), monitor those reports too.
  
• Sender score/reputation: There are services that can give you insights into your sender reputation. Google’s Postmaster, for example, will tell you if your domain or IP reputation is high, medium, low, or bad in Gmail’s view, as well as spam complaint rates, etc. If you see reputation dipping, it’s a prompt to take corrective action (like tightening your list or pausing to let things recover). Some tools even give you a composite “score” out of 100. While you don’t need to obsess over a single number, these can be useful for catching issues early. Regularly check your reputation – it’s like checking your credit score for email. If something looks off, investigate it.
  
• Use deliverability testing tools: Aside from metrics from your own sends, you can use external tools to test before and after sending. For example, some services allow you to send an email to a panel of test addresses at various ISPs and then show you if those landed in inbox or spam, and why (they often provide spam filter feedback). These tools can be great to run on a new template or a particularly important email to catch problems beforehand. They might flag issues like missing authentication, your domain being on a blacklist, or content that looks phishy. If you do find your domain or IP on a blacklist (through such tests or via a site like mxtoolbox), you’ll need to investigate removal – but preventing that via good practices is the best approach.
  
• Track deliverability across segments: If you have multiple types of emails (newsletters, transactional, marketing blasts) or different segments, monitor them separately. You might find, for instance, that your cold prospecting emails have worse deliverability than your customer newsletters. This insight lets you apply targeted fixes (maybe the prospecting needs more warming up or list vetting). Many companies separate their mail streams on different IPs/domains to protect their core mail from issues in another stream – that’s an advanced strategy, but something to know as you grow.
  

Using Poptin Popups to Build an Engaged Email List

Growing your email list is important, but how you grow it directly impacts your deliverability. Engaged, interested subscribers lead to higher open rates and fewer complaints—both essential for strong deliverability. On the other hand, adding random or uninterested contacts can hurt your sender reputation. One of the most effective ways to attract high-quality subscribers is through website popups, and Poptin specializes in making this process seamless.

With Poptin, you can create various types of popups and control exactly when they appear—whether on exit intent, after a set time, or upon scrolling. The goal is to convert website visitors into email subscribers in a user-friendly, non-intrusive way. When implemented strategically, popups can significantly boost your list growth and engagement.

For instance, the digital agency Okisam leveraged Poptin’s popups and saw a 42% increase in email subscription conversions in just one month! (Read more here: How Okisam Achieved 42% Boost in Email Signups in a Month – Poptin)

By using smart, targeted popups, you can grow a high-quality email list that enhances engagement and improves deliverability.

Conclusion

Email deliverability may seem technical, but it ensures your emails reach people who genuinely want them. Good sending practices help, like authentication, maintaining a strong sender reputation, keeping your list clean, and creating engaging content.

These steps significantly increase your chances of reaching inboxes instead of spam folders. Improving deliverability is ongoing, but the rewards include higher open rates, better engagement, and more successful campaigns.

Using smart tools makes a difference. For example, Poptin popups help grow your subscriber base by converting interested visitors into engaged subscribers, boosting email deliverability.

Successful email deliverability comes down to this: send emails people love and follow best practices. Doing so builds a positive sender reputation and helps you consistently reach your audience. Implement these strategies, track your metrics, and set yourself up for long-term success.

Ready to boost your email marketing results? Sign up for Poptin for free today!

Damilola Oyetunji

Content Writer.