Email Deliverability Audit: A Step-by-Step Guide for Marketers

If your emails land in spam, your automation workflows fail. An email deliverability audit finds the root cause. This guide walks through each step — from DNS checks to content scoring — so you can fix issues and improve inbox placement.

What is an email deliverability audit?

An email deliverability audit is a systematic review of everything that affects whether your emails reach the inbox. It covers authentication records (SPF, DKIM, DMARC), sender reputation (blacklists, bounce rates), list hygiene, and content quality. The goal is to identify gaps that cause spam placement and take corrective action.

You should run an audit quarterly or before launching high-volume campaigns. Think of it as a health check for your email program.

Step 1: Check your SPF record

SPF (Sender Policy Framework) tells receiving servers which IPs are authorized to send email for your domain. A missing or misconfigured SPF record is one of the most common reasons for deliverability problems.

To audit your SPF record, query your domain’s DNS with a tool like dig or an online SPF checker. Look for the v=spf1 tag. Your record should list all sending sources — your ESP, web servers, third-party tools — and end with ~all (softfail) or -all (hardfail). Avoid +all — it authorizes any server to send from your domain.

Common mistakes: duplicate SPF records (only one allowed), missing include statements for third-party senders, and forgetting to update when you add a new sending tool. Tip: if you exceed the ten DNS lookup limit, you’ll need to consolidate includes or use subdomains.

Step 2: Verify DKIM signatures

DKIM (DomainKeys Identified Mail) adds a digital signature to your emails. Receiving servers verify this signature against a public key in your DNS. If the signature is missing or invalid, your emails may be flagged as spam or rejected.

Audit DKIM by sending a test email to a DKIM checker tool. Check that the d= value matches your domain, the selector is correct, and the signature passes validation. Your ESP usually provides the DKIM selector and public key — confirm you’ve added the right TXT record.

If you use multiple sending systems, each may need its own DKIM selector. Many marketers forget to set up DKIM for transactional emails, which is a mistake because transactional emails often carry password resets or order confirmations. Verify that your transactional provider also supports DKIM signing from your domain.

Step 3: Review your DMARC policy

DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM. It tells receiving servers what to do if an email fails both checks: none (do nothing), quarantine (send to spam), or reject (block).

During your audit, check your DMARC record. It should be a TXT record at _dmarc.yourdomain.com. Start with p=none to monitor reports, then move to p=quarantine or p=reject once you’re confident all legitimate mail authenticates. Also set rua and ruf to an email address where you receive aggregate and forensic reports. These reports help you spot unauthorized senders using your domain.

A DMARC policy of reject is the strongest protection against spoofing. It also signals to mailbox providers that you take deliverability seriously. Many large senders require at least quarantine.

Step 4: Scan your sender reputation

Your sender reputation is a score mailbox providers assign to your sending IP and domain. It’s based on factors like bounces, spam complaints, and blacklist presence.

To audit reputation, check your IP and domain against major DNS blacklists (DNSBLs) like Spamhaus, Barracuda, and SURBL. Use a multi-list checker tool. If you appear on a blacklist, follow that list’s removal process. Some blacklists automatically delist after you fix the issue; others require a manual request. Keep records of your remediation steps in case you need to appeal.

Also review your bounce and complaint rates. A bounce rate above 5% signals poor list hygiene. Complaint rates above 0.1% can get you blocked by Gmail and Outlook. Use feedback loops from major ISPs to track complaints. If you see a spike in complaints, look at recent campaigns and subscriber sources.

Step 5: Analyze engagement and list hygiene

Mailbox providers look at how recipients interact with your emails. Low open rates, low clicks, and many unopened messages hurt your reputation. A clean list improves deliverability.

Audit engagement by segmenting your list: active (opened in last 30 days), lapsed (30-90 days), and inactive (90+ days). Send re-engagement sequences to lapsed subscribers. Remove or suppress inactive addresses if they don’t re-engage after three months.

Also check for hard bounces and role accounts (like admin@ or info@). Remove them immediately. Hard bounces indicate invalid addresses — if you keep sending to them, your reputation suffers. Use double opt-in to prevent junk addresses from entering your list in the first place.

Step 6: Test inbox placement

Inbox placement tests use seed lists to show where your email lands across different providers (Gmail, Outlook, Yahoo, etc.). These tests give you a real-world view of deliverability.

Use a seed-based testing tool. Send a campaign and review the results. If your email lands in spam for Gmail, check your authentication and content. Placement can vary by provider, so look at the breakdown. For example, Gmail may block due to user-level reports while Outlook flags content.

Run tests periodically, especially after changing infrastructure or content templates. Track trends over time. A sudden drop in inbox placement often points to a recent change in authentication or sending behavior.

Step 7: Score your email content

Spam filters score your email content for red flags. High spam scores cause blocked delivery even if authentication passes.

Check your content against common spam triggers: excessive use of sales words (free, buy now, limited time), all-caps subject lines, too many images with little text, and broken HTML. Use a spam score checker to get a numeric score and identify specific issues. Aim for a score below 4 on most checkers.

Also review your sending frequency. If your emails go out too often or too rarely, engagement can drop. Find a consistent cadence that works for your audience. A/B test subject lines and preheaders to improve open rates.

Step 8: Validate your sending infrastructure

Beyond authentication, check your mail server configuration. Verify that your reverse DNS (PTR record) matches the hostname you send from. Most receiving servers require a valid PTR record for the sending IP. Without it, your emails may be delayed or rejected.

Also confirm that your sending IP has a good history. New IPs need warm-up: start with low volume and gradually increase. If you share an IP with other senders (common with shared ESP plans), their reputation can affect yours. Consider a dedicated IP if you send high volumes.

Create a remediation plan

After the audit, prioritize fixes based on impact. Start with authentication (SPF, DKIM, DMARC) — these are foundational. Then address blacklisting and reputation issues. Finally, optimize content and list hygiene.

Document each issue and the action you took. That record helps you track progress and prove good practices if you ever need to appeal a block. For more on automation workflows, see our guide on building triggered email sequences for LTV.

A thorough audit every quarter keeps your deliverability healthy. That means more inbox placement, more engagement, and better LTV from your automated workflows.

Frequently asked questions

How often should I run an email deliverability audit?

Run an audit at least once per quarter. Increase frequency to monthly if you send high volumes, have recently changed sending infrastructure, or have experienced a deliverability issue. Also audit before launching a major campaign.

What is the most important step in a deliverability audit?

Checking your SPF, DKIM, and DMARC records is the most critical step. Without proper authentication, your emails are likely to be marked as spam or rejected. Fixing authentication issues often resolves deliverability problems quickly.

How do I check if my domain is on a blacklist?

Use a multi-IP and domain blacklist checker tool. Enter your sending IP and domain. The tool queries major DNSBLs like Spamhaus, Barracuda, and SURBL. If listed, follow the delisting instructions provided by each blacklist operator.

What is a good spam score for email content?

Aim for a spam score under 3 out of 10. Scores above 5 may cause delivery issues. Spam checkers provide a numeric score and highlight problematic words, structures, or HTML elements. Lower the score by reducing sales language, balancing images with text, and testing your HTML.

Can DMARC policy affect deliverability even if I don’t have SPF or DKIM issues?

Yes. A DMARC policy of ‘none’ shows you are not enforcing authentication. Some mailbox providers may treat unenforced domains with lower trust. Moving to ‘quarantine’ or ‘reject’ signals you actively protect your domain, which can improve deliverability over time.