Email deliverability challenges keeping you up at night? You're not alone. Maintaining spotless email domain health has never been more critical to your outbound success.
Your email domain is the cornerstone of successful email marketing campaigns. Think of it as the foundation of your digital communication infrastructure – without a solid foundation, even the most compelling email content won't reach your audience's inbox.
Achieve 100% deliverability rates by focusing on what we here at Folderly call the "Six Building Blocks of Email Domain Health." These aren't just recommendations – they're non-negotiable requirements for any serious email marketer in 2025.
What You'll Learn in This Guide
- DNS Authentication Setup: Master DKIM, SPF, DMARC, and BIMI configuration
- Reputation Monitoring: Prevent and resolve blacklist issues before they hurt your campaigns
- Technical Infrastructure: Optimize SMTP settings and domain architecture
- Domain Strategy: Choose the right domain structure for maximum trust
- Reputation Management: Monitor and improve your sender reputation
- Advanced Troubleshooting: Identify and fix complex deliverability issues
Step 1: DNS Authentication Records: Your Digital ID
Email authentication has transformed dramatically since 2020, with major ISPs now mandating proper DNS authentication for inbox placement. These four critical records work together as your domain's digital passport, proving legitimacy to receiving servers:
Sender Policy Framework (SPF)
SPF acts as your domain's bouncer, explicitly listing which mail servers are authorized to send emails on your behalf. With phishing attacks targeting 86% of organizations, a properly configured SPF record is your first line of defense.
How to check SPF:
- Go to MXToolbox.com
- Select "SPF Record Lookup" from the dropdown menu
- Enter your domain name (example.com)
- Click "SPF Lookup" to see your current record
- Look for "SPF record found" - this means you have an SPF record set up
Critical Reminder: Every new email service you integrate requires SPF record updates. Missing this step can immediately harm your deliverability. The best way to update it quickly is with our free SPF Generator. Also, make sure your SPF record doesn't exceed the 10 DNS lookup limit.
DomainKeys Identified Mail (DKIM)
DKIM functions as your email's digital signature, creating an encrypted fingerprint that receiving servers use to verify your identity. Without proper DKIM setup, your emails are vulnerable to spoofing and more likely to land in spam folders.
How to check DKIM:
- Open Gmail and send a test email to your own Gmail account
- Open the received email and click the three dots menu
- Select "Show original"
- Look for the DKIM field – you want to see "PASS" status
If you want to dive deeper and learn how to address potential issues, here’s a detailed guide from our experts on how to check DKIM Record.
Domain-based Message Authentication, Reporting and Conformance (DMARC)
DMARC is your email authentication orchestrator, coordinating DKIM and SPF while providing valuable reporting on authentication failures. Major email service providers now prioritize DMARC-compliant senders for inbox placement.
DMARC Implementation Strategy:
- Start with a monitoring policy (p=none) to gather data
- Gradually move to quarantine (p=quarantine) then reject (p=reject)
- Set up email reports to track what's happening with your emails
- Review these reports regularly to catch anyone trying to impersonate your domain
How to check: Just like with SPF, you can use the online DMARC Record Check by MXToolbox to check your current DMARC record and identify potential problems. You can dive deeper to learn what is DMARC record in detail with our comprehensive guide. Also, we encourage you to generate a valid record with Folderly's DMARC generator.
Brand Indicators for Message Identification (BIMI)
BIMI displays your company logo directly in recipients' inboxes, providing visual authentication and increasing brand recognition. As the evolution of email authentication, BIMI requires a strong DMARC policy and, in many cases, a Verified Mark Certificate (VMC).
How to check: BIMI checkup is available on MXToolBox as well. Just type your domain name and get a quick overview of your BIMI record's current state.
Step 2: Checking Blacklist Listing
Email blacklists have become more sophisticated, with real-time updates and granular categorization. Being listed can devastate your deliverability overnight, making proactive monitoring essential.
Modern Blacklist Landscape:
- IP-based blacklists for shared and dedicated IPs
- Domain-based blacklists targeting sending domains
- Content-based blacklists analyzing email patterns
- Behavioral blacklists monitoring engagement metrics
Comprehensive Monitoring Approach: Use multiple monitoring services to cover all major blacklists including Spamhaus, Barracuda, SpamCop, SURBL, and emerging regional blacklists. Automated alerts ensure immediate notification of any listings.
How to check: Head over to MxToolBox or Blacklist Alert, two great platforms, for a swift and efficient blacklist check. While manually visiting every major blacklist is an option, these blacklist monitors can evaluate your domain against all major and minor blacklists within seconds:
Step 3: SMTP Configuration and Testing
Simple Mail Transfer Protocol (SMTP) is your email delivery engine – the system that actually moves your messages from your server to recipients' inboxes. When SMTP isn't configured properly, you'll face hard bounces (permanent failures), soft bounces (temporary delays), or silent delivery failures where emails disappear without any notification.
Essential SMTP Health Checks:
- Port connectivity testing: Verify ports 587 (secure submission), 465 (SSL), and 25 (standard) are accessible
- Authentication verification: Confirm your username/password login works correctly
- TLS/SSL encryption: Ensure secure connections protect your email data in transit
- Connection timeout settings: Test retry logic handles temporary connection issues properly
- Bounce handling: Verify failed delivery notifications reach you for list management
Advanced SMTP Considerations: Modern email infrastructure requires IPv6 support for future compatibility, proper reverse DNS (PTR records) to match your IP with domain name, and connection pooling optimization to handle high-volume sending efficiently without overwhelming receiving servers.
Step 4: Strong Redirect Setup
By redirecting links in your email to your main site, you reinforce the connection between the email and your domain. This can help establish a positive email sender reputation over time, as consistent branding and traffic patterns indicate legitimate and trustworthy communication. Also, it enhances brand recognition and familiarity, provides a seamless user experience and increases engagement promotes consistency and transparency, making you stop asking, “Why are my emails going to spam?”
Contrary to this, if you include links in your email that direct recipients to unfamiliar or unrelated websites, it may raise suspicions of phishing or spoofing. This can trigger spam filters or cause recipients to mark your emails as spam.
➡️ What to do: Double-check whether all your domains and subdomains lead to the main website. While redirecting to the main site can be beneficial for email deliverability, it's important to ensure that your main site and landing pages are secure, mobile-friendly, and provide relevant and valuable content to the recipients.
Step 5: Review Your Domain Levels
In large organizations, every department or division may include a unique third-level domain that can act as a simple yet effective, way of identifying that particular department. Various third-level domain names are used to balance the load on sites with heavy traffic.
A third-level domain is the next highest level, following the second-level domain in the domain name hierarchy. It is the segment that is found directly to the left of the second-level domain. The third-level domain is often called a “subdomain”, and includes a third domain section in the URL.
What to do:
Make sure you use trustworthy domains. Here’re recommendations from our tech team:
- .com/ .io / .co — the most trustworthy domains (such domains are strongly associated with great email domain health)
- .net /.org — the domains with strong levels of trustworthiness
- All other domains are associated with less strong email domain health
Step 6: Check Your Current Domain Reputation
Tools like Folderly help you quickly check your current domain reputation and assign an email deliverability score for your potential campaigns. You can get a quick overview of key issues with your domain and address the problems before they negatively affect your email domain's health.
What to do: Read the full article on how to test email deliverability or just check email deliverability in a few clicks.
Bottom Line: It’s All About Comprehensive Approach
Checking the six critical components discussed in this article will give you a clear picture of your current email deliverability state. However, to ensure optimal deliverability and maintain a successful email marketing strategy, it is crucial to take a comprehensive approach to email domain health.
While we discussed key building blocks, there are other important things to check, such as email list hygiene, spam trigger words, sending frequency, email compliance, and other crucial things to address that may help prevent email from going to spam.
And, to truly unlock the potential of your email campaigns, consider harnessing the expertise of professional email deliverability consulting services offered through dedicated customer success managers. With the guidance of customer success managers, you can navigate the intricate web of sender authentication, list hygiene, engagement metrics, and technical infrastructure management with ease. They will equip you with the tools and strategies to conquer deliverability challenges and optimize your email domain health.
