Email Deliverability Audit: A Step-by-Step Checklist to Find and Fix Delivery Problems

Most deliverability problems don't announce themselves. An email that should reach the inbox quietly ends up in spam, gets silently deferred, or gets caught on a blocklist nobody noticed. By the time the impact shows up in open rates or business results, the underlying issue has often been building for weeks.

A deliverability audit is how you find those problems before they compound. Running through a structured checklist every quarter — or any time you notice a decline in performance — gives you a clear picture of where your sending setup stands and exactly what needs attention.

Step 1: Verify Your Authentication Records

Authentication is the foundation. Start here before anything else.

• SPF: Check that your SPF record includes all servers and services that send email on your behalf. Common gaps: a marketing platform added since the record was last updated, a new SMTP relay not yet authorized, or transactional email providers sending from your domain. Also verify your record doesn't exceed the 10 DNS lookup limit — records over the limit fail silently.
• DKIM: Confirm DKIM signatures are present on outbound mail and that the public key in DNS matches the private key your mail server is signing with. If keys were recently rotated, verify old selectors have been removed and new ones have propagated.
• DMARC: Confirm a DMARC record is published and review your DMARC aggregate reports for sources sending under your domain that you didn't authorize. An unrecognized sending source in DMARC reports signals either a misconfigured system or an active spoofing attempt.

Step 2: Check Reverse DNS and PTR Records

Every IP address your mail server sends from should have a PTR record resolving to a valid, descriptive hostname, and that hostname should resolve back to the same IP (forward-confirmed reverse DNS). Many receiving servers check this, and missing or mismatched PTR records are a consistent cause of legitimate email being filtered. If you've added sending IPs recently, PTR records are a common omission.

Step 3: Run Blocklist Checks

Check your sending IPs and domain against major blocklists: Spamhaus SBL, XBL, and PBL; Barracuda; SORBS; and SpamCop. A listing on any of these affects delivery to ISPs that query those feeds. If you find a listing, follow the removal process specific to each list — and identify the underlying cause before requesting delisting, since re-listing without a root-cause fix is common. The blocklist removal guide covers this in detail.

Step 4: Review Bounce and Complaint Rates

Pull your bounce and complaint data for the past 30 days. Look for:

• Hard bounce rate above 2%: Addresses that don't exist should have been removed from your list long before reaching this threshold. High hard bounces indicate list hygiene problems that need immediate attention.
• Repeated soft bounces from the same domain: This often signals a reputation issue with that specific ISP rather than a temporary server problem.
• Complaint rate above 0.10%: Google's published threshold for Gmail. Anything above this actively harms your Gmail delivery. Ensure that all complainers are immediately suppressed via your suppression list.

Step 5: Run an Inbox Placement Test

Authentication passing and blocklists clean doesn't guarantee inbox placement. Run an inbox placement test using a seed list service to see where your messages actually land across Gmail, Outlook, Yahoo, and other major providers.

If you're hitting spam at one provider but not others, the problem is specific to how that ISP perceives your sending reputation — not a universal authentication failure. That distinction tells you where to focus your remediation.

Step 6: Assess Your List Hygiene

• When did you last remove subscribers who haven't opened mail in 6 months?
• Are hard bounces being suppressed within 1–2 send cycles?
• Do you have a re-engagement flow before sunsetting inactive subscribers?
• Are new subscribers collected via confirmed opt-in, or are contacts imported without address verification?

A clean list is not a secondary concern. Sending to disengaged or invalid addresses is one of the most direct ways to build negative sender reputation over time. The decay is gradual until it suddenly isn't.

Step 7: Check Content and Compliance

• Verify all marketing email includes a functional, one-click unsubscribe — required by Gmail and Yahoo for bulk senders
• Confirm your From address uses your actual domain, not a freemail provider
• Run sample email through a spam content scoring tool to surface content-level issues
• Verify your sending IPs have a working abuse contact in WHOIS and/or an active postmaster address

Step 8: Verify BIMI Configuration

If you're relying on BIMI for brand visibility in Gmail and Yahoo inboxes, check that it's still working correctly. BIMI requires an enforced DMARC policy — if your logo has stopped appearing, the first thing to check is whether your DMARC policy has drifted from p=reject back to p=none.

Making This a Quarterly Practice

A deliverability audit shouldn't only happen during a crisis. The time investment is modest compared to diagnosing a reputation problem that's already in progress. Schedule it quarterly, assign clear ownership to one person, and document findings each time so trends become visible across multiple reviews.

The goal is to catch small problems while they're still small — before a blocklist listing becomes a sustained reputation hit, before a rising complaint rate reaches the threshold that triggers active filtering, before an authentication misconfiguration has been quietly failing for months.

Use MailDog's SMTP infrastructure and DNS security tools as part of your ongoing monitoring stack. For guidance on a specific deliverability issue you've uncovered, the support team can help you work through it.