You've built the perfect email. The copy is compelling, the design is beautiful, the call-to-action is irresistible. You hit send to your 50,000 subscribers and wait for the conversions to roll in. But something's wrong. Open rates are half what they used to be. Click rates have cratered. Revenue from email is down 40%.
Your emails aren't broken. They're just not arriving.
This is the deliverability problem, and it catches more companies off guard than almost any other aspect of email. You can have the best email program in the world, but if your messages land in spam—or worse, get blocked entirely—none of it matters.
Deliverability vs. delivery
First, let's clear up a common confusion. 'Delivery rate' and 'deliverability' are not the same thing.
Delivery rate measures whether the receiving server accepted your email. If you send 1,000 emails and 950 are accepted (with 50 bouncing), your delivery rate is 95%. Most email platforms report this metric, and most senders obsess over it.
But delivery rate is misleading. An email can be 'delivered' and still end up in spam. The receiving server accepted it—that counts as delivered—but then their spam filter looked at it and decided it wasn't worthy of the inbox. From the recipient's perspective, they never got your email.
Deliverability is about inbox placement: what percentage of your delivered emails actually reach the inbox versus spam or promotions folders. This is much harder to measure (you can't directly see where emails land) and much more important for your results.
A sender with 99% delivery rate but 50% inbox placement is in serious trouble. Half their emails are effectively invisible. Meanwhile, a sender with 95% delivery rate but 95% inbox placement is doing great—the 5% that bounced were probably bad addresses anyway.
The reputation game
Email providers like Gmail, Outlook, and Yahoo don't just filter individual emails—they build profiles of senders and use those profiles to make filtering decisions. This is your sender reputation, and it's the single biggest factor in deliverability.
Reputation is tracked at multiple levels. Your IP address has a reputation. Your domain has a reputation. Even specific email addresses can have reputations. These reputations are built over time based on how recipients interact with your email.
Positive signals include: recipients opening your emails, clicking links, replying, moving emails from spam to inbox, and adding you to contacts. Negative signals include: recipients marking you as spam, deleting without reading, and low engagement overall.
The math is unforgiving. If 0.1% of recipients mark your email as spam, that's a warning sign. If 0.3% do, you're in trouble. If 0.5% do, you might be blocked entirely. These thresholds seem tiny, but at scale they represent real patterns of recipient dissatisfaction.
Reputation is also sticky. Build a bad reputation, and it takes months of good behavior to recover. This is why deliverability problems often seem to come out of nowhere—you've been slowly damaging your reputation for months, and suddenly you cross a threshold where filters start blocking you.
Authentication as table stakes
Ten years ago, you could have decent deliverability without email authentication. Today, it's non-negotiable.
SPF, DKIM, and DMARC are the baseline. If you're not authenticating your email, major providers will treat you with suspicion regardless of your content or reputation. It's not that authentication guarantees inbox placement—it doesn't—but lack of authentication almost guarantees spam placement.
Beyond the basics, there are additional authentication signals that help. BIMI displays your logo next to authenticated emails, building brand recognition. MTA-STS ensures your email connections are encrypted. These aren't required, but they signal that you take email seriously.
Authentication also protects your reputation from spoofing. If someone sends spam pretending to be from your domain, and you don't have DMARC enforcement, that spam damages your reputation. Proper authentication ensures only your legitimate email affects your reputation.
The content trap
There's a persistent myth that deliverability is primarily about content—avoid certain words, don't use too many images, keep your HTML clean. This was true 15 years ago. It's much less true today.
Modern spam filters are sophisticated machine learning systems. They don't just look for 'FREE' in the subject line. They analyze patterns across millions of emails, considering sender reputation, recipient behavior, content characteristics, and dozens of other signals. Gaming them with content tricks is a losing battle.
That said, content isn't irrelevant. Certain patterns are still red flags: excessive use of URL shorteners, too many links, image-only emails with no text, and content that looks like known spam templates. But these are more about not looking like spam than about magic words to avoid.
The real content factor is engagement. If your content is relevant and valuable, recipients engage with it. That engagement builds reputation. If your content is irrelevant or annoying, recipients ignore it or mark it as spam. That destroys reputation. The best content strategy for deliverability is simply sending emails people want to receive.
List hygiene: The unsexy essential
Nothing kills deliverability faster than a dirty list. And almost every company's list is dirtier than they think.
Hard bounces—emails to addresses that don't exist—are the most obvious problem. Sending to invalid addresses signals that you're not maintaining your list, which is a spam indicator. Most email platforms automatically remove hard bounces, but you need to make sure this is actually happening.
Spam traps are addresses specifically designed to catch spammers. Some are recycled addresses that were once valid but have been abandoned and repurposed. Others are 'pristine' traps that were never valid—they exist only to catch people who scrape or buy lists. Hitting spam traps devastates your reputation.
Inactive subscribers are a subtler problem. Someone who signed up three years ago and hasn't opened an email since is hurting your engagement metrics. Low engagement signals to filters that your email isn't wanted. Regularly pruning inactive subscribers—or at least segmenting them into a less frequent cadence—protects your reputation with engaged subscribers.
The hardest list hygiene problem is role addresses and shared inboxes. An email to [email protected] might be read by different people at different times. If one of them marks you as spam, it affects your reputation even though others at that company want your email. There's no perfect solution, but being aware of the risk helps.
Monitoring and recovery
Deliverability problems are easier to prevent than to fix, which means monitoring is essential. By the time you notice declining open rates, the damage is already done.
Track your key metrics over time: delivery rate, open rate, click rate, spam complaint rate, unsubscribe rate. Look for trends, not just absolute numbers. A gradual decline in open rates over several months is a warning sign even if the current rate seems acceptable.
Use seed testing to monitor inbox placement. Services like GlockApps or 250ok maintain test addresses at major providers. You send to these addresses, and they report where your email landed. This gives you direct visibility into inbox vs. spam placement that you can't get from your own metrics.
Check blacklists regularly. Being listed on a major blacklist like Spamhaus can tank your deliverability overnight. Most blacklist listings are the result of specific incidents—a spam complaint spike, hitting a spam trap—and can be resolved by fixing the underlying problem and requesting delisting.
If you do end up with deliverability problems, recovery is a slow process. You need to identify and fix the root cause, then rebuild reputation through consistent good behavior. This typically means reducing volume, focusing on your most engaged subscribers, and gradually expanding as metrics improve. There are no shortcuts.
Frequently asked questions
What's a good inbox placement rate?
For transactional email, aim for 95%+. For marketing email, 85-90% is good, 90%+ is excellent. Below 80% indicates serious problems. These numbers vary by industry and audience.
How long does it take to fix deliverability problems?
Weeks to months, depending on severity. Minor issues might resolve in 2-4 weeks of good behavior. Major reputation damage can take 3-6 months to recover from. There's no way to speed this up significantly.
Should I use a dedicated IP or shared IP?
Dedicated IPs give you full control over your reputation but require enough volume to build reputation (typically 100k+ emails/month). Shared IPs pool reputation across senders, which can help low-volume senders but exposes you to others' bad behavior.
Why did my deliverability suddenly drop?
Common causes: hitting a spam trap, spike in complaints, blacklist listing, authentication misconfiguration, or sending to a purchased/old list. Check your DMARC reports, blacklist status, and recent changes to your sending practices.