Improve Email Deliverability: Here’s How & Best Practices to Follow

Hitting the inbox is paramount, no matter how big or small a sender you are. 

If not…

1. Your marketing campaigns go unseen. 
2. Your transactional emails fail to reach their destination. 
3. Your efforts translate into lost revenue and damaged sender reputation.

At Mailtrap, we help you improve deliverability with your organically built audience, whether it’s for marketing campaigns or critical transactional communications. 

This comprehensive guide walks you through the essential strategies and best practices that high-volume senders use to achieve optimal inbox placement and maximize their email ROI.

How to improve email deliverability: a snapshot

Achieving high email deliverability is an ongoing process that requires a strategic approach across technical setup, sender reputation, list management, and content optimization. 

Here’s a quick overview of the quick wins we’ll explore in detail:

Email deliverability improvement strategies

Achieving consistent inbox placement for your high-volume sends demands a multi-faceted approach. 

• Email infrastructure setup
• Sender reputation
• email list quality
• email sending 
• email content quality
• email user engagement

I will break down each aspect into an actionable how-to. Let’s start with the technical improvements.

Improve email infrastructure

To improve email infrastructure, you need to focus on email authentication, domain configuration, and email security.

It will show Internet Service Providers (ISPs) and mailbox providers that your emails are legitimate and secure. And actually, all major ISPs require authentication protocols if you’re to be considered a legitimate sender ➡️(Gmail, Outlook, Yahoo, and Apple Mail). 

I’ll explain what you should check in your current setup, why this matters, and what steps you need to take to improve your inboxing rates.

Email authentication protocols

Double-check the protocols’ setup and fix the following if you identify any issues. 

• SPF (Sender Policy Framework): Check your SPF record with Mailtrap’s Free SPF Record Checker. If an email originates from a server not listed in your SPF record, it’s likely to be flagged as suspicious or spam.
• DKIM (DomainKeys Identified Mail): Utilize Mailtrap’s Free DKIM Record Checker to validate your setup.
• DMARC (Domain-based Message Authentication, Reporting & Conformance) builds on SPF and DKIM. For large senders, it helps gain visibility into spoofing attempts. Use our Free DMARC Record Checker to ensure that DMARC is correctly configured.
• BIMI (Brand Indicators for Message Identification): Display your brand’s logo next to your authenticated emails in the recipient’s inbox. While not directly a deliverability protocol, BIMI enhances brand recognition and user trust, indirectly boosting engagement. 

For a deeper dive into authentication, refer to our guide on Email Authentication Explained: SPF, DKIM, DMARC, BIMI.

DNS records for email sending

Proper DNS configuration ensures your email servers are correctly identified and email can be routed effectively. So, here’s your homework 😀

• rDNS (Reverse DNS or PTR records): Maps an IP address back to a domain name, acting as a “reverse lookup.” ISPs often check PTR records to ensure the sending IP is legitimate and not a generic or dynamic address, which helps prevent spam.
• MX records (Mail Exchange records): Specify the email servers responsible for accepting email messages on behalf of your domain. Okay, these are primarily for inbound email, but correctly configured MX records indicate a professionally managed domain, lending credibility to your outbound emails.

Custom domain configurations

Use custom configurations instead of the generic ones provided by your Email Service Provider. Here are the customizations to make. 

• Custom return path (MAIL FROM): Use a custom subdomain (e.g., bounces.yourdomain.com) for your return path to ensure that bounce handling doesn’t negatively impact your main sending domain’s reputation and allows for easier tracking.
• Custom tracking URLs: If your ESP uses tracking links (for opens, clicks), ensure these are branded with your domain (e.g., clicks.yourdomain.com). This avoids sharing reputation with your ESP’s generic tracking domain and instills greater trust in recipients and filters.

Email transmission security standards

Secure emails in transition to protect sensitive data and signal trustworthiness to mailbox providers. This is what to do 🔽

• TLS (Transport Layer Security) / STARTTLS: Most ISPs require and prefer TLS connections. You should always enforce STARTTLS where possible.
• MTA-STS (Mail Transfer Agent Strict Transport Security): A security standard that forces email servers to use TLS when sending email. It helps prevent downgrade attacks where an attacker might force a connection to use unencrypted channels. Mailtrap’s blog has an in-depth guide on the Mail Transfer Agent (MTA) Explained.
• TLS-RPT (TLS Reporting): Companion to MTA-STS, TLS-RPT allows you to receive reports on TLS connection issues, providing visibility into potential security problems that could affect deliverability.

Further reading: STARTTLS vs SSL vs TLS Explained

Mailbox provider Feedback Loop (FBL)

Subscribe to FBLs (e.g., through Google Postmaster Tools or Microsoft SNDS) to quickly identify and remove complainers from your list. Of course, this prevents further complaints that damage your reputation. 

For more details on the feedback loop, check: What Is Email Feedback Loop and Why Is It Important?

Email Headers

Properly configured email headers provide necessary information for email servers and can influence how your emails are processed and delivered.

• Message ID: Most times, it’s automatically generated. However, ensure it’s correctly formatted and present to help with email tracking and debugging.
• Date header: Accuracy here is important for chronological sorting and filter evaluation. So, check these headers particularly if you operate in different time zones. 
• List-unsubscribe header: Make sure this header provides a one-click unsubscribe option directly within the email client interface. New sender requirements mandate it, and it genuinely helps with spam complaints. Learn more about its importance: List Unsubscribe Header: Why and How to Use.
• Precedence header: Used to indicate the nature of an email (e.g., precedence: bulk or precedence: junk) to inform receiving servers that it’s a bulk email and should not generate auto-replies. While less common now, it can still have an impact.

Use a reliable email service provider

If you handle transactional and marketing campaigns at a volume, a reliable Email Service Provider (ESP) is essential. Check whether the ESP provides the necessary technical infrastructure to ensure your emails consistently reach recipients’ inboxes.

For instance, Mailtrap Email API/SMTP offers a robust infrastructure designed for high-volume senders. We focus on maximum throughput and optimal inbox placement by leveraging the following:

• Automatic email authentication: Mailtrap configures and manages essential authentication protocols (SPF, DKIM, DMARC). This process verifies your emails as legitimate, significantly reducing the likelihood of them being flagged as spam or rejected by receiving servers.
• Dedicated sending streams: Mailtrap provides separate, isolated sending streams for different email types (e.g., transactional vs. marketing). This prevents potential deliverability issues from spilling from one email type to another (marketing to transactional and vice versa).
• Robust security and compliance: We are compliant with regulations such as ISO 27001 and GDPR, ensuring your data and your recipients’ privacy are protected.

Improve sender reputation

Your sender reputation encompasses your IP reputation and domain reputation. It’s a critical factor ISPs use to determine whether your emails reach the inbox or are sent to the spam folder. Check the key aspects you need to consider. 

IP reputation management

The reputation of the email-sending IP address (or addresses) directly impacts your deliverability. Here’s what to keep in mind. 

• Shared vs. dedicated IP:
  • Shared IP address: When choosing an ESP, make sure they adhere to the security protocols and have internal mechanisms to weed out spammers. Ideally, like Mailtrap, the provider should offer separate sending streams for different types of messages.
  • Dedicated IP address: If you send more than 100K emails a month, I’d encourage you to choose a dedicated IP address. It gives you complete control over the IP reputation and allows for more precise IP warming. You can check more on the topic: Shared vs Dedicated IP in Email Sending.
• IP warming & re-warming: When you get a new dedicated IP or significantly change your sending practices (like introducing a new domain, subdomain, or a third-party service for cold emails), you must gradually increase your sending volume. This is the IP warm-up, building trust with ISPs over time. Re-warming is necessary if you have periods of inactivity or significant changes in volume. 

• IP pooling strategies: If you send at high volumes (e.g., 1M+ emails a month) or have diverse email streams, use multiple dedicated IPs grouped into “IP pools.” This strategy allows you to distribute the sending load and isolate different types of email (e.g., transactional vs. marketing) to separate IPs, protecting the reputation of critical streams.
• IP segmentation by email stream (Reminder): Send different types of emails (e.g., transactional, marketing, notifications) from separate dedicated IPs or subdomains to isolate their reputations. If your marketing emails encounter issues, your critical transactional emails remain unaffected. 
• IP blocklist monitoring: Regularly check if your sending IPs have been listed on any public or private blocklists. ISPs use these lists to identify and block email from suspicious sources. You can use Mailtrap’s Free IP Blacklist Checker to monitor your IP status.
• IP delisting process: If your IP gets blocklisted, promptly follow the delisting procedures of the specific blocklist provider. This typically involves identifying and rectifying the root cause of the listing (e.g., spam complaints, spam traps) and then requesting removal.

Email domain reputation management

Similar to your IP, the reputation of your sending domain is crucial because it represents your brand’s trustworthiness, which is often expressed through a sender score.

• Domain warming techniques: As a reminder, new sending domains or subdomains benefit from a gradual increase in sending volume, especially to highly engaged recipients.
• Subdomain strategy for isolation: Using distinct subdomains for different email streams (e.g., marketing.yourdomain.com, transactional.yourdomain.com, newsletter.yourdomain.com) allows you to compartmentalize reputation. If marketing.yourdomain.com faces email performance issues, transactional.yourdomain.com remains unaffected.
• Google Postmaster Tools insights: This free tool from Google provides valuable data on:
  • Your sending domain’s reputation 
  • IP reputation 
  • Spam rate 
  • Authentication and delivery errors for Gmail recipients. 

Regularly monitoring these insights is critical for proactive reputation management. 

• Microsoft SNDS data usage: Microsoft’s Smart Network Data Services (SNDS) provides similar insights for Outlook.com and other Microsoft properties. It offers data on spam complaints, filtered emails, and overall reputation, helping you troubleshoot deliverability issues specific to Microsoft inboxes.
• Consistent domain branding: Ensure your “From” address, custom tracking domains, and custom return-path domains all consistently use your primary sending domain or closely related subdomains. This consistency builds brand recognition and trust. You can also use Mailtrap’s Free Domain Blacklist Checker to monitor your domain’s status.

Recipient engagement impact on reputation

Recipient engagement is a powerful signal to ISPs about the quality and relevance of your emails. High positive engagement boosts your reputation, while negative email engagement can quickly degrade it.

• Positive engagement signals: Keep an eye on opens, clicks on links within the email, replies, marking an email as “not spam,” and adding your “From” address to their address book. ISPs interpret these actions as signs that recipients value your emails.
• Negative engagement signals: The most damaging are spam complaints. Other negative signals include deleting emails without opening them, unsubscribing, and emails bouncing back as undeliverable.
• Engagement-based segmentation: Segment your email list based on engagement levels (e.g., highly engaged, moderately engaged, inactive). Send your most valuable content to your most engaged segments to reinforce positive reputation signals. Also, create reengagement campaigns to motivate other, less-engaged segments. 
• Effective sunset policies: Implement policies to gradually reduce or stop sending to consistently unengaged subscribers. Sending to inactive users generates low engagement and can accumulate negative signals over time, harming your overall deliverability, particularly if you send a large volume of emails.

Reputation recovery strategies

If your sender reputation takes a hit, a systematic approach is needed for recovery. So, don’t panic, but do the following.

• Diagnose root cause of damage: Identify why your reputation suffered. Was it a sudden spike in spam complaints, high bounce rates, or a blocklisting? Utilize tools like Google Postmaster Tools, SNDS, and DMARC reports to pinpoint the issue.
• Create a step-by-step recovery plan: This might involve pausing sends, removing problematic subscribers, re-engaging cautiously, or appealing blocklist entries.
• Communication with ISPs/blocklist owners: In some cases, direct communication with the relevant ISP postmaster teams or blocklist operators may be necessary after you’ve addressed the underlying issues. Be prepared to explain the steps you’ve taken to resolve the problem.
• Gradual re-warm and ramp up the volume: Reestablish your sending reputation slowly after addressing the root cause. Begin with highly engaged segments and gradually increase volume, monitoring email deliverability rate closely. This is similar to the initial IP warming process, but with an added focus on demonstrating sustained good behavior. 

Improve email list management

Your email list is your most valuable asset in email marketing. Maintaining its quality and relevance is essential for consistently good email deliverability. Here, I will explain what you should do to improve the quality of your email list and why you should do it. 

Optimize list acquisition methods

The journey to high deliverability begins the moment you acquire a subscriber, where quality over quantity is the golden rule. So, when a new subscriber comes knocking on your door, focus on the following.

• Permission-based opt-ins: Always ensure you have explicit permission from every subscriber. This means they’ve actively agreed to receive emails from you. Avoid any pre-checked boxes.
• Clear consent mechanisms (GDPR focus): The opt-in forms must clearly state what the subscriber is signing up for, how often they’ll hear from you (e.i, the number of emails per week/month), and what kind of content to expect. For users in regions with strict data protection laws like GDPR, ensure consent is freely given, specific, informed, and unambiguous. (To stress, it’s a legal requirement, not a nice-have 😀)
• Transparent data usage statements: Clearly communicate your privacy policy and how subscriber data will be used (data security at rest and in transit). This builds trust and sets expectations, reducing the likelihood of spam complaints later.
• Source quality validation: Implement processes to monitor and validate the source of your new subscribers. This helps identify and eliminate any channels that might inadvertently bring in low-quality or non-consenting leads.
• Avoiding purchased or rented lists: Never! Lemme say that again, NEVER 😀, under any circumstances, purchase or rent email lists. These lists are notorious for containing spam traps, inactive addresses, and non-consenting users, leading to immediate and severe damage to your sender reputation and deliverability.

Implement effective opt-in processes

The method you use to onboard new subscribers directly affects the quality and engagement of your list. Therefore, I’d like to dissect opt-ins further to give you an actionable framework you can apply right away.

• Single opt-in (SOI) vs. double opt-in (DOI) strategies:
  • Single opt-in (SOI): Subscribers are added to your list immediately after filling out a form. While quicker for the user, it carries a higher risk of invalid addresses or accidental sign-ups.
  • Double opt-in (DOI): Subscribers receive a confirmation email that they must click to verify their subscription. This is the gold standard for high-volume senders, as it guarantees consent, confirms email validity, and leads to significantly higher engagement and deliverability rates.
• DOI confirmation email design and timing: Your DOI email should be clear, concise, and sent immediately after sign-up. Its design should be simple, with a prominent call-to-action to confirm the subscription. It’s a transactional email, actually. 
• Managing and storing consent records: Maintain auditable records of when and how each subscriber provided consent. This is crucial for compliance with data protection regulations and for demonstrating legitimacy to ISPs if questioned.
• Welcome email for new subscribers: Send a timely welcome email to new subscribers. This reinforces their decision, sets expectations, and provides initial value, kickstarting positive engagement.

Advanced list hygiene techniques

Proactive list cleaning is vital to prevent bounces, reduce spam complaints, and protect your sender reputation from degradation.

So, buckle up and employ the following email deliverability best practices:

• Automate hard bounce removal rules: Implement automated systems to remove hard-bounced email addresses from your list immediately. Hard bounces indicate permanent delivery failures and negatively impact your reputation. For more on this, see Email Bounce Explained: Definition, Reasons, Best Practices
• Monitor soft bounces and establish retry logic: Monitor soft bounces (temporary delivery issues) and implement a retry strategy (e.g., a couple of retries in an hour or two after the initial bounce). If an address soft bounces repeatedly, consider temporarily suppressing or removing it after a defined number of failures. Check out our blog post to learn more about the Difference Between Hard and Soft Bounce.
• Detect and mitigate spam traps proactively: Spam traps are invalid email addresses used by ISPs to identify spammers. Hitting them severely damages your reputation. Regularly clean your list and scrutinize acquisition sources to avoid them. For more details, read ➡️ What is a Spam Trap: Guide for Email Marketers and Software Developers.
• Using list validation and cleaning services: Consider using third-party email list validation and cleaning services for large lists. Better yet, if you got programming skills or have a dev team to back you, consider baking an API validation and sanitization into your lead-capture backend. Whichever way, these tools can identify invalid, risky, or low-quality email addresses before you send to them. Read our expert tips on Email List Cleaning: Best Practices from an Expert.

Strategic list segmentation for relevance

Segmentation improves deliverability by ensuring your emails are relevant to your audience, leading to higher engagement.

• Segmentation by engagement levels: Yeah, I know, I begin sounding like a broken record. But anyway, group subscribers based on their interaction with your emails (e.g., highly engaged, moderately engaged, unengaged). This allows you to tailor content and sending frequency.
• Demographic and psychographic segmentation: Segment based on subscriber demographics (age, location) or psychographics (interests, values) to deliver more targeted content.
• Behavioral segmentation (website activity, purchase history): Create segments based on user behavior on your website, purchase history, or in-app actions. This enables highly relevant, triggered, or personalized communications.
• Dynamic list segmentation techniques: Implement systems that automatically update segments based on real-time user behavior, ensuring your lists are always current.

Personalization based on segments: Leverage your segmentation data to personalize email templates, content, subject lines, and offers, making each email feel more tailored to the individual. For a full tutorial, check ➡️Email List Segmentation Explained: Tutorial with Examples.

Wrapping it up

We hope you enjoyed reading about how to improve email deliverability. This article was originally published on the Mailtrap Blog, where you can find the full version along with many other helpful resources.