Email marketing remains one of the most effective digital channels, offering a return on investment (ROI) that outperforms most others. But no matter how compelling your content is or how finely tuned your audience targeting, none of it matters if your emails don’t actually reach your recipients. This is where email deliverability comes in. It is a critical, often misunderstood component of successful email marketing.
This guide breaks down what email deliverability is, why it matters and how you can maximise your chances of landing in the inbox instead of the spam folder.

What is Email Deliverability?
Email deliverability refers to the ability of an email to successfully reach the recipient’s inbox. It is distinct from delivery rate, which simply indicates whether an email was accepted by the recipient’s server. A message can be "delivered" but still end up in the spam or junk folder, which is not considered a success in marketing terms.
Deliverability depends on a combination of technical setup, sender reputation, list hygiene and user engagement.
Why is Deliverability So Important?
If your emails aren't getting into inboxes, your marketing is essentially invisible. Poor deliverability leads to:
- Reduced engagement, like opens and clicks
- Lower ROI
- Damage to sender reputation
- Missed opportunities to engage and convert
Even a small drop in deliverability can result in significant revenue loss. For example, if your list has 100,000 subscribers and your inbox placement drops from 95% to 85%, that equates to 10,000 people who aren’t seeing your emails i.e. 10,000 people who you can’t convert through email messaging.
The Factors That Influence Deliverability
Deliverability is influenced by a complex ecosystem of signals and standards. The most important include:
1. Sender reputation
Internet Service Providers (ISPs) evaluate your sender reputation to determine whether to deliver your emails. Key elements that affect reputation:
- Spam complaints: High complaint rates are a red flag.
- Bounce rate: Too many invalid addresses lower trust.
- Blacklisting: If your domain or IP is on a blocklist, expect major deliverability issues.
- Engagement rates: Emails that are opened, read and clicked improve reputation.
2. Authentication protocols
Setting up authentication tells ISPs that your email is legitimate. Essential protocols include:
- SPF (Sender Policy Framework): Verifies that your IP is authorised to send emails for your domain.
- DKIM (Domain Keys Identified Mail): Adds a digital signature to your email headers.
- DMARC (Domain based Message Authentication, Reporting & Conformance): Helps domain owners prevent spoofing by aligning SPF and DKIM.
3. Content and formatting
Certain types of content are more likely to trigger spam filters:
- Excessive use of capital letters, exclamation points or spammy phrases (“Buy now!”, “Free!”, “Risk free!”)
- Heavy image to text ratios
- Large attachments
- Broken or misleading links
4. List Quality and hygiene
Using outdated, purchased or poorly maintained lists can destroy your deliverability. Best practices include:
- Regularly removing inactive subscribers
- Verifying new sign ups through double opt in
- Avoiding rented or third party lists
5. Sending behaviour
ISPs notice erratic or aggressive sending patterns.
- Sudden spikes in volume may look suspicious.
- Inconsistent timing damages trust.
- High frequency can lead to fatigue and unsubscribes.
Best Practices to Improve Email Deliverability
Improving deliverability isn't a one time fix; it's a continuous process. Here are actionable strategies:
1. Authenticate your email domain
Implement SPF, DKIM, and DMARC as early as possible. Most reputable email marketing platforms (like Mailchimp, SendGrid or ActiveCampaign) provide tools and tutorials for setting this up.
2. Warm up your IP and domain
When using a new IP or domain for sending, ramp up your volume gradually, don’t flood ISPs with high sends. This allows ISPs to observe your behavior and build trust.
Example warm up schedule:
- Day 1–3: Send to 1,000 – 2,000 highly engaged contacts
- Day 4–7: Increase to 5,000 – 10,000
- Continue growing based on engagement and performance
3. Practice list hygiene
Remove invalid, unengaged and bounced email addresses regularly. Use email verification tools to clean lists before importing them into your platform.
Key metrics to monitor:
- Bounce rate: Should stay below 2%
- Unsubscribe rate: Ideally under 0.5%
- Spam complaints: Should stay under 0.1%
*Benchmarks vary by industry. If you require specific benchmarks, feel free to reach out to our .
4. Use double opt in
Double opt in ensures that only genuinely interested users get on your list. It also drastically reduces fake signups (including bots) and improves engagement metrics.
5. Segment your list
Personalised, targeted emails perform better than mass sends. Segmentation by behavior, location or past engagement can lead to higher opens, clicks and lower complaint and unsubscribe rates.
6. Create engaging content
Emails that are opened and interacted with signal to ISPs that your messages are valuable.
Tips:
- Write compelling subject lines (but avoid spam triggers)
- Optimise for mobile
- Include a clear CTA (call to action)
- Use plain text alternatives alongside HTML versions
7. Monitor your sender reputation
Use tools like:
These platforms can alert you to blacklisting, reputation issues and other red flags.
Common Email Deliverability Pitfalls
Avoid these mistakes that commonly sabotage email campaigns:
❌ Buying email lists
Purchased lists often contain spam traps, invalid emails and unengaged users, leading to blacklisting and high complaint rates.
❌ Ignoring engagement
If subscribers consistently don’t open your emails, ISPs will start filtering your messages as spam.
❌ Failing to monitor metrics
Without tracking your key performance indicators (KPIs), you’ll miss the warning signs of deliverability problems.
❌ Sending without consent
Under laws like GDPR and CAN SPAM, sending unsolicited emails can result in legal action and damage to your brand’s reputation.
The Role of Email Service Providers (ESPs)
Your ESP plays a big role in your deliverability. Good ESPs offer:
- Built in authentication tools
- Deliverability monitoring
- Automated bounce and complaint handling
- Shared or dedicated IPs
Tip: For large scale senders, a dedicated IP gives more control over sender reputation, but only if you can maintain consistent volume and hygiene.
Measuring Email Deliverability Success
Here are some of the key metrics to focus on:
- Inbox Placement Rate (IPR): % of emails delivered to inboxes vs. spam folders
- Open Rate: Signals user interest; impacted by deliverability
- Bounce Rate: Should be below 2%; hard bounces are especially harmful
- Spam complaint rate: Should stay below 0.1%
- Click To Open Rate (CTOR): Shows how compelling your email is once opened
If you're seeing low open rates, high bounce rates or frequent spam complaints, you may have a deliverability issue.
Final Thoughts
Email deliverability is the foundation of effective email marketing. It’s not just a technical hurdle, it’s a strategic priority. Even the most beautifully designed campaign will fall flat if your message ends up in the spam folder or never reaches the intended recipients.
By proactively managing your reputation, maintaining list hygiene and adhering to best practices in content and frequency, you can build a strong deliverability track record and maximise the impact of your email efforts.
Remember: Think of deliverability as a long term investment. Every email you send is a data point that builds or breaks your sender reputation.