Email Deliverability – How to Improve It in 2025?

Email deliverability can make or break your email marketing success, yet many businesses struggle with it without even realizing why their messages aren’t reaching the inbox.

Low deliverability leads to emails getting trapped in spam folders, high bounce rates, and poor engagement, all of which mean wasted time, lost revenue, and damaged sender reputation.

In this blog, learn about

• What affects email deliverability?
• Best email marketing deliverability rate to aim for
• How to increase email deliverability.

What is email deliverability?

Email deliverability refers to the ability of an email message to successfully reach a recipient’s inbox, rather than being blocked or filtered into spam or junk folders.

It’s a measure of how effectively your emails get through the complex filtering systems set up by email service providers (ESPs) to protect users from unwanted or harmful messages.

Why is email deliverability important?

Email deliverability is important because if your emails don’t reach the inbox, your messages remain unseen, meaning lost opportunities for engagement, conversions, and customer retention.

Poor email marketing deliverability can damage your sender reputation, making it even harder to get future emails delivered.

What is the best email marketing deliverability rate?

The email deliverability rate measures the percentage of emails you send that successfully land in recipients’ inboxes, not in spam or bounce.

Excellent Deliverability

A deliverability rate of 95% or higher is considered best-in-class. This means that at least 95 out of every 100 emails you send successfully reach the inbox.

Good Deliverability

Rates between 90% to 95% are solid and typical for well-maintained lists and reputable senders.

Below Average

Anything below 85 – 90% signals issues such as poor list quality, authentication problems, or spam complaints, which require immediate attention.

Factors Affecting Email Deliverability

A combination of technical, behavioral, and content-based factors determines whether your email campaigns are successfully delivered.

Below is a deep dive into the most critical factors affecting email deliverability, backed with real-world examples and insights.

1. Sender Reputation (IP & Domain)

In email marketing, your sender reputation is like a credit score for your email sending behavior. It’s determined by ISPs (like Gmail, Outlook) based on your history of sending patterns, including spam complaints, bounces, engagement rates, and more.

A low reputation leads to emails getting sent to spam or being rejected altogether. A strong sender reputation increases inbox placement.

Example: If you send bulk emails to unverified lists, leading to high bounce rates and spam complaints, your reputation score drops. Gmail may start flagging your domain, hurting all future email campaigns.

2. Email Authentication (SPF, DKIM, DMARC)

These protocols authenticate your emails, proving they come from your domain, not a spammer spoofing your address.

• SPF: Verifies sending IPs are authorized.
• DKIM: Adds an encrypted signature to emails.
• DMARC: Sets policies for how ISPs should handle unauthenticated emails.

Without authentication, your marketing emails are more likely to be marked as spam or blocked outright.

3. List Quality and Hygiene

The health of your email list, including how valid, recent, and engaged your subscribers are, has a direct impact on email deliverability.

A list full of invalid emails, unengaged users, or spam traps leads to bounces, low engagement, and even blocklisting.

Example: A business that purchased an email list experiences a high bounce rate and sees its campaigns marked as spam, resulting in blocked sends from Gmail and Yahoo.

4. Engagement Metrics (Opens, Clicks, Spam Complaints)

ISPs monitor how users interact with your emails.

High engagement = inbox. Low engagement or spam complaints = spam folder.

ISPs use engagement to decide if your content is wanted. High open and click rates increase your email deliverability, while ignored emails hurt it.

Example: If 80% of your recipients don’t open your emails for 3 months, ISPs start deprioritizing your sends, even if your content is clean.

5. Sending Frequency and Volume

How often and how many emails you send at once impact email marketing deliverability. Sudden volume spikes or overly frequent emails can raise flags with ISPs.

Inconsistent or excessive sending patterns can trigger rate limiting or blocking, especially from providers like Gmail and Outlook.

Example: A brand that sends one email per month suddenly sends daily promotions during Black Friday without warming up, and their emails start landing in spam.

6. Email Content and Design

The actual words, structure, and visuals in your emails impact your email deliverability. Spammy content or improper formatting can affect whether your email lands in the inbox or spam.

Spam filters scan your content for red flags like ALL CAPS, too many images, spammy phrases (“Buy now!”), or missing unsubscribe links.

Example: An email with a flashy design, no plain-text version, excessive images, and a “GET RICH FAST!!!” subject line will likely go straight to spam.

7. IP and Domain Blocklisted

Blocklisted are real-time databases that track domains/IPs known for sending spam. If your sender IP or domain appears on one, your email deliverability decreases.

Most ISPs automatically reject or filter emails from blocklisted IPs.

Example: Using a shared IP with other businesses, you get blocklisted because another sender on the same IP was flagged for spam.

8. Bounce Rate (Hard & Soft Bounces)

A bounce is when your email can’t be delivered.

• Hard bounces = permanent issues (invalid email).
• Soft bounces = temporary (e.g., full inbox, server error)

High bounce rates suggest poor list quality, which signals spammy behavior to ISPs.

Example: Sending to an old, stale list results in 15% bounce rate. Your ESP flags your account, and future sends are throttled.

How to improve email deliverability?

From technical settings to content best practices, even small missteps can hurt your sender reputation and block your emails from ever being seen.

The strategies to improve email deliverability are:

1. Authenticate your domain: SPF, DKIM, and DMARC
2. Maintain a clean and engaged email list
3. Segment your audience and send relevant content
4. Optimize your email frequency and timing
5. Avoid spam triggers in subject lines and content
6. Include a clear and easy-to-find unsubscribe link
7. Use a recognizable sender name and email address
8. Warm up your sending IP and domain
9. Keep your email list growth organic

Let’s see these ways to increase email deliverability in detail

1. Authenticate your domain: SPF, DKIM, and DMARC

Authentication protocols prove that your emails are genuinely from you, preventing spoofing and phishing. Without them, many ISPs (Internet Service Providers) treat your emails suspiciously.

How to do it:

• SPF (Sender Policy Framework): Specifies which mail servers are authorized to send emails on your behalf.
• DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails to verify authenticity.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): Helps ISPs decide how to handle emails failing SPF or DKIM.

These terms might sound scary, but with an email marketing software like Retainful, you can verify your domain in a few clicks and increase email deliverability.

2. Maintain a clean and engaged email list

Sending emails to invalid, outdated, or inactive addresses results in bounces and spam complaints and hurts your sender reputation and you will start getting email deliverability issues.

How to increase email deliverability by cleaning the email list:

• Regularly remove hard bounces (permanent failures) immediately.
• Suppress or re-engage inactive subscribers who haven’t opened emails in 3-6 months.
• Use double opt-in to ensure subscribers genuinely want your emails.

Example: If you have 10,000 subscribers but 30% never open emails, removing or re-engaging them improves your engagement metrics and deliverability.

3. Segment your audience and send relevant content

Segment your customers based on demographics, purchase history, email engagement, and life-cycle stage, and send personalized emails.

By doing targeted email marketing and sending relevant emails you get better engagement (opens, clicks), signaling to ISPs that your emails are wanted.

How to do it:

Segment your email list by:

• Past purchase behavior
• Engagement level (active vs inactive)
• Demographics or location
• Preferences or interests

Example: To improve email deliverability, send a re-engagement email campaign only to inactive users, and a VIP offer to your best customers instead of blasting one generic email.

4. Optimize your email frequency and timing

Sending automated emails too often or at the wrong times increases unsubscribes and spam complaints, decreasing email marketing deliverability.

How to improve email deliverability by timing emails:

• Find a sending cadence that balances staying top-of-mind without overwhelming subscribers.
• Use engagement data to send emails when recipients are most likely to open (e.g., Tuesdays at 10 AM).
• Avoid sudden spikes in volume and gradually increase sending if you have a new list.

Example: A weekly email newsletter might work better than daily blasts for your audience. Testing time slots can increase open rates and email marketing deliverability.

5. Avoid spam triggers in subject lines and content

Certain words, phrases, and formatting trigger spam filters, lowering your chances of emails landing in your inbox.

How to increase email deliverability with non-spammy email content:

• Avoid words like “Free,” “Buy now,” “Urgent,” or excessive punctuation (!!!).
• Keep subject lines clear, concise, and personalized.
• Limit the use of all caps and too many images.
• Balance text-to-image ratio (at least 60% text).
• Ensure your emails include a plain-text version.

Example: Instead of “BUY NOW!!! LIMITED TIME FREE OFFER,” try “Special offer just for you – 20% off this week only.”

6. Include a clear and easy-to-find unsubscribe link

To fix email deliverability, provide an easy way to unsubscribe and reduce spam complaints. This keeps your email list healthy.

How to do it:

• Always place the unsubscribe link in the footer.
• Make the process simple – avoid extra steps or forcing users to log in.
• Remind subscribers what they signed up for (optional but helpful).

7. Use a recognizable sender name and email address

Familiar sender info builds trust and encourages opens. Generic or suspicious sender details can get emails flagged or ignored.

How to improve email deliverabilty with sender details:

• Use your brand or a clear person’s name.
• Avoid “noreply@” addresses.
• Keep it consistent across campaigns.

Example: “Sarah from [Brand]” is more engaging than “sales@[brand].com” or “noreply@[brand].com.”

8. Warm up your sending IP and domain

If you’re sending emails from a new IP or domain, ISPs may distrust you at first. Warming up builds a reputation gradually.

How to do it:

• Start by sending small volumes to your most engaged subscribers.
• Gradually increase volume over days or weeks.
• Monitor bounce and complaint rates closely.

Example: Sending 100 emails per day initially and doubling every few days until you reach your target volume.

9. Keep your email list growth organic

Buying email lists or harvesting emails from shady sources leads to poor deliverability and potential blocklisting.

How to do it:

• Use opt-in sign-up forms on your website, social media, and events.
• Offer incentives like discounts or free resources in exchange for signups.
• Use double opt-in to confirm subscribers’ intent.

Example: A pop-up on your e-commerce site offering 10% off for signing up generates quality leads who want your emails.

How to Monitor Email Deliverability?

Monitoring email deliverability is essential to catch issues early, maintain inbox placement, and ensure your campaigns perform as intended.

1. Track key email marketing metrics

Start by regularly reviewing these core deliverability indicators in email marketing metrics:

• Bounce rate: High bounce rates (especially hard bounces) can signal a list quality issue or domain block.
• Open rate: A sudden drop might mean emails are landing in spam.
• Click-through rate (CTR): Low CTR combined with low opens may indicate poor inbox placement.
• Unsubscribe and complaint rates: High rates here damage your sender reputation and signal audience dissatisfaction.

2. Use Deliverability Monitoring Tools

Platforms like Postmark, Mailtrap, Mailgun, Litmus, or Validity’s Everest offer advanced monitoring features, including inbox placement tests, spam filter testing, and blocklisting checks. These tools give you visibility into how mailbox providers are treating your emails.

3. Monitor Sender Reputation

Your domain and IP reputation affects email deliverability. Check them using tools like:

• Google Postmaster Tools – Offers insights into Gmail reputation, spam rate, and authentication.
• Microsoft SNDS – For feedback from Microsoft inboxes.

4. Run Inbox Placement Tests

Inbox placement testing lets you send test emails to a variety of inboxes (Gmail, Yahoo, Outlook, etc.) to see where they land – inbox, spam, or not at all. This helps you understand how different providers treat your emails.

Wrapping up!!

Email deliverability isn’t a set-it-and-forget-it task, it’s an ongoing process that requires attention, testing, and adaptation. Always monitor your sender reputation, keep your lists clean, and prioritize sending value-driven content your audience actually wants to receive.

To improve email marketing deliverability, focus on building trust with both your audience and inbox providers. Send relevant content, clean your list regularly, and stay compliant with authentication protocols.

Frequently Asked Questions