You send an email. Your recipient never sees it. It's not in their spam folder either - it just vanished into the void. This happens more often than most people realize, and the cause is almost always something fixable. You just need to know where to look.
An email deliverability audit sounds intimidating. But most of it comes down to checking a handful of things that directly influence whether inbox providers trust you enough to let your messages through. You don't need to be a developer or a sysadmin to do this. You need a methodical approach and a few free tools.
Here's how to work through it, step by step.
Start With Your Authentication Records
Authentication is the foundation of email deliverability. If your domain hasn't set up the right DNS records, inbox providers have no way to verify that the emails claiming to come from you actually do. That uncertainty alone is enough to send your messages straight to spam.
There are three records worth checking: SPF, DKIM, and DMARC.
SPF tells receiving mail servers which servers are allowed to send email on behalf of your domain. If you send from multiple platforms - like a marketing tool, a CRM, and your regular email host - each one needs to be listed. A broken or incomplete SPF record is one of the most common deliverability problems.
DKIM adds a cryptographic signature to your outgoing emails. It lets the receiving server verify that the message wasn't tampered with in transit. If your email provider doesn't walk you through setting this up, it's worth checking whether it's active.
DMARC ties SPF and DKIM together and tells inbox providers what to do when an email fails authentication. Even setting it to a basic monitoring-only policy (p=none) is better than having nothing in place.
To check all three, use a free tool like MXToolbox or dmarcian. Type in your domain, run the lookups, and read the results. Red or warning flags usually come with plain-English explanations of what's wrong. You can then share those results with your DNS provider or email host to get things corrected. For a deeper look at how DNS underpins all of this, see our DNS management overview.
Check Your Sender Reputation
Your domain and your sending IP both have reputations. Inbox providers track them over time, and a poor reputation means your messages get filtered before anyone ever reads them. As we covered in How Sender Reputation Works and Why It Is the Foundation of Email Deliverability, this score is built gradually - and damaged quickly.
To check where you currently stand, use these free tools:
- Google Postmaster Tools - If a meaningful portion of your recipients use Gmail, this is essential. It shows your domain reputation, spam rates, and authentication pass rates. It's free, but you need to verify ownership of your domain first.
- Sender Score (by Validity) - Gives your sending IP a score from 0 to 100. Anything below 70 is worth investigating.
- Talos Intelligence - Cisco's tool that shows whether your IP is flagged as poor, neutral, or good.
If your reputation is low, the fix usually comes down to reducing spam complaints, removing bad addresses from your list, and sending more consistently to people who actually want your emails. There's no shortcut - reputation improves over time with better sending habits.
Run a Blacklist Check
Blacklists are databases of IP addresses and domains that have been flagged for sending spam. If you land on one, your emails may be blocked outright by any mail server that consults that list.
The good news is that checking is easy. MXToolbox has a free blacklist checker that queries dozens of the major lists simultaneously. Enter your sending IP address and it tells you immediately whether you appear on any of them.
If you find yourself listed, don't panic. Most blacklists have a removal request process. The bigger question is why you got listed, because if you don't fix the underlying cause, you'll land on the list again. Common reasons include a sudden spike in email volume, high complaint rates, or sending to a list with too many invalid addresses.
Test What Inbox Providers Actually See
Authentication records can look fine on paper but still cause deliverability problems in practice. The best way to check is to send a real test email and see what happens to it.
Mail-tester.com is one of the most useful free tools for this. It gives you a temporary address to send a test email to, then scores the message out of 10 based on authentication, content, blacklist status, and formatting. The report is detailed enough to be actionable without being overwhelming.
GlockApps and Mailtrap offer similar functionality, with some paid options for more detailed inbox placement testing across multiple providers.
Send a message that looks like your typical outgoing email - not a blank test. The content matters too, and you want results that reflect what your recipients will actually receive.
Audit Your List and Sending Habits
The technical side of email deliverability is only part of the picture. How you build and maintain your list has just as much influence on whether your emails land in the inbox.
Go through your mailing list and ask these questions:
- When did you last remove hard bounces? Every address that permanently bounces and stays on your list drags your sender reputation down. As we explored in How Bounce Rates Silently Destroy Your Email Deliverability Over Time, this damage compounds quietly over months.
- Are there addresses you haven't sent to in over a year? Old, unengaged contacts are more likely to mark you as spam or be converted into spam traps. Segment them and run a re-engagement campaign before deciding whether to keep them.
- Do you have a clear unsubscribe process? If recipients can't easily opt out, they hit the spam button instead. That complaint rate directly affects your reputation.
- Are you sending at a consistent volume? Sudden spikes - like going from 500 emails a week to 50,000 - trigger spam filters. If you're scaling up, warm up your sending volume gradually.
Review Your Email Content
Spam filters don't just look at who sent the email. They also analyze what's inside it. Some content patterns are strongly associated with spam, and even legitimate senders can trigger filters accidentally.
A few things to check in your email templates:
- Your text-to-image ratio. Emails that are mostly images with very little text look suspicious. Aim for a balance - roughly 60% text, 40% images is a reasonable guideline.
- Misleading or overly promotional subject lines. ALL CAPS, excessive exclamation marks, and phrases like "FREE!!!" still trigger filters at many providers.
- Link quality. If you're including links, make sure the domains you're linking to aren't blacklisted. A link to a spam-flagged domain can hurt your own deliverability.
- The from address. Sending from a no-reply address like no-reply@yourdomain.com doesn't directly hurt deliverability, but it discourages replies - and engagement signals do matter over time.
Set a Schedule and Keep Checking
A one-time audit is useful, but email deliverability isn't a set-and-forget problem. Blacklists change. Your IP reputation fluctuates. Lists go stale. DNS records can get accidentally overwritten during a hosting migration.
Running a light version of this audit every quarter - checking your authentication records, running a blacklist scan, and reviewing your bounce and complaint rates - keeps problems from building up silently. The first time you catch a blacklisting or a broken DKIM record before a major campaign goes out, you'll be glad you made it a habit.
You don't need to understand every technical detail to do this well. You just need to know which tools to run, what the results mean, and when to ask for help fixing something. Most of it is genuinely approachable once you break it down into these steps.
