Inbox or spam? The must-know email deliverability rules for marketers
Email marketing remains the most lucrative channel for brands. According to Marigold’s 2025 Consumer Trends Index, more respondents made a purchase from an email (54%) than from any other channel, including social media ads (44%) or posts (43%), SMS/MMS messages (26%), mobile app alerts (22%), and banner ads (17%).
Today’s consumers expect seamless experiences across channels, which means that (over)relying on just one channel is risky. However, as the number one channel, email deserves special attention. And it all starts with the inbox. Even the most well-crafted campaign is ineffective if it never reaches the inbox.
Why does deliverability matter?
Mastering email deliverability best practices is essential for successful email marketing. Without it, brands miss opportunities to engage meaningfully with their customers, drive conversions, and maximize revenue. Marketers must proactively manage deliverability to ensure messages consistently land in inboxes, not spam folders.
Did you know that more than 347.3 billion emails are sent to subscribers across the globe every day? Not all of those emails will eventually reach inboxes. Around 85% either go to spam folders or are blocked. Internet Service Providers or ISPs evaluate messages to determine inbox placement to protect their users and networks.
It’s not just unsolicited emails or messages with malicious content that are blocked or flagged as spam. Many marketing messages that subscribers genuinely want to receive end up in spam folders daily. That’s why it is essential for all email marketers to understand how to build and maintain strong deliverability.
What is deliverability, and how is it different from delivery rate?
Deliverability and delivery rate are often mistaken for the same thing, but there is an important difference.
Delivery rate is the percentage of emails successfully accepted by an ISP.
Deliverability is the percentage of emails that reach the inbox instead of spam.
Email deliverability refers to the ability to deliver an electronic message to the recipient’s inbox using a valid email address.
Spam refers to unsolicited, irrelevant, or bulk electronic messages, often sent for advertising. However, what’s classified as spam is also about perception: what one recipient sees as unwanted, another may find valuable. When recipients actively interact with your emails, they signal that your messages are wanted, helping to improve your reputation and, in turn, your deliverability. The good news? Perception and reputation can evolve, and by focusing on engagement, you can ensure your emails reach the inbox.
The cost of poor deliverability
Here’s proof that email deliverability directly impacts business success. When one Marigold client faced inbox placement issues that lowered their open rates, their daily revenue dropped by 11.5%.
Internal team changes led to practices that were misaligned with deliverability best practices. Thanks to Marigold’s proactive monitoring and dedicated deliverability experts, we quickly identified the issue, contacted our client’s team, and provided the guidance needed to get them back on track. At Marigold, we aim to do more than fix deliverability issues: We empower brands with the knowledge and tools to maintain strong inbox placement and protect revenue.
Inbox placement and revenue have a symbiotic relationship, as illustrated by this image showing a client’s sends over one month.
Poor deliverability leads to lost revenue, reduced engagement, and wasted marketing spending. For marketers who want to maximize performance, it’s clearly worth taking on an active role in improving inbox placement. Your conversion and engagement rates will thank you.
Email deliverability best practices to keep your emails inbox-ready
There are many confusing technical terms and practices related to deliverability, but marketers should also focus on more familiar aspects, such as maintaining a high-quality email list, best practices for message content, and fostering strong engagement with subscribers. Here are the best practices our deliverability team recommends.
Authenticate your emails: What we do at Selligent
Implement SPF, DKIM 2048, and DMARC: These authentication protocols verify sender identity and help prevent spoofing.
Monitor domain reputation: ISPs prioritize domain reputation over IP reputation. Follow best practices to maintain a strong sender reputation.
Monitor complaint rates: Keep an eye on your spam complaint rates.
Avoid sudden volume spikes: Gradually ramp up sending when using a new domain or IP to build trust with ISPs.
Create Feedback Loop (FBL): When recipients mark your email as Spam, it negatively impacts your reputation as a sender. You can address this by enrolling in the Complaint Feedback Loop. Each ISP has its own FBL. This means the spam complaint is converted to an unsubscribe, which is a lot less damaging to your reputation.
Marketing cadance and engagement
Manage marketing cadance: Overloading subscribers with too many emails can lead to increased complaints and unsubscribes. Within Selligent there are granular send limits and prioritisation that marketers can use to ensure recipients are not overmailed. Even better, allow recipients to control how often they hear from you through a preference center.
Balance promotional and informational content: Alternating between sales-driven messages and editorial or educational content helps keep engagement high and reduces fatigue.
Monitor complaint rates: Keep spam complaints below 0.1%, as higher rates negatively impact sender reputation and inbox placement.
Encourage positive engagement: Prompt subscribers to add your sender address to their contact list and interact with emails by including clear calls-to-actions (CTAs).
Maintain a clean and engaged list
Collect data responsibly: Always obtain explicit permission from subscribers and use double opt-in to confirm genuine interest.
Monitor engagement: Only send emails to active users who have opened or clicked within the last 3-6 months.
Avoid spam traps: Never purchase email lists and regularly validate addresses to remove invalid or high-risk contacts.
Simplify unsubscribing: A visible and easy-to-use unsubscribe link reduces complaints and improves sender reputation.
Manage dormant accounts
Run re-engagement campaigns: Send targeted messages to inactive subscribers to encourage interaction.
Sunset non-engaged contacts: Remove dormant subscribers to protect deliverability if re-engagement efforts fail.
Use preference centers: Allow subscribers to customize email frequency and content type to maintain engagement.
Optimizing email content for deliverability
Use clear and recognizable sender information: Ensure your sender name and email address are easily identifiable to build trust and reduce spam complaints.
Optimize subject lines: Keep subject lines concise, engaging, and free from excessive punctuation or spammy language. Use A/B testing regularly to find which words and phrases are the most engaging for you audience.
Balance text and images: Avoid emails that are entirely image-based, as ISPs may flag them as spam. Ensure a good mix of HTML and text content.
Ensure mobile responsiveness: Many recipients check emails on mobile devices. Use responsive design to optimize readability across screens and facilitate engagement.
Avoid the use of URL shorteners such as bitly or t.co and third-party-hosted images: These are often associated with spammers and can hurt your deliverability.
Provide clear unsubscribe options: Make it easy for recipients to opt out to prevent spam complaints.
Avoid misleading tactics: Do not use deceptive subject lines, fake reply indicators, or urgent-sounding language that can trigger spam filters.
Test before sending: Use inbox preview tools to check how emails render across different email clients and devices.
Monitor key metrics
Reliable KPIs: Track deliverability, click-through, unsubscribe, and complaint rates to gauge email performance.
Unreliable KPIs: Click rates and open rates require some caution.
Click rates can be inflated through non-human interactions, such as bots and ISPs checking that links in an email are safe.
Be cautious with open rates due to Mail Privacy Protection, which can inflate engagement data. Overall trends in open rates are a good indicator, but don’t take them too literally. Watch for any significant dips in open rates across all major ISPs. A notable dip at one ISP without a dip at the others is a strong indicator of an inboxing issue you’ll need to address.
How Selligent helps marketers maintain strong deliverability
If you use a cross-channel marketing hub like Selligent, you can benefit from the services of a dedicated deliverability team. Selligent’s in-house deliverability specialists provide proactive monitoring and expert support to help marketers maintain inbox placement. Our team:
Monitors deliverability 24/7, identifying and resolving issues before they affect performance.
Provides dedicated, multilingual support (EN, FR, ES, IT, PT, DU).
Stays ahead of evolving ISP requirements to ensure compliance and optimize inbox placement.
Conclusion
Email deliverability is the foundation of a high-performing email strategy. Marketers can improve inbox placement by prioritizing list hygiene, optimized message content, and engagement.
Don’t let deliverability issues derail your email marketing success. Contact our team to learn more about how Selligent’s deliverability experts can help you optimize your inbox placement.
