Email deliverability

What deliverability is

Email deliverability is whether your email reaches the inbox, as opposed to the spam folder or nowhere at all. The catch most people miss: "delivered" does not mean "inboxed."

It helps to separate two terms that sound alike. Your delivery rate only tells you the receiving server accepted the message and it did not bounce. Deliverability, sometimes called inbox placement, is what happens next: of the mail that was accepted, how much actually reached the inbox versus being filtered into spam. An email can be accepted, counted as delivered in your dashboard, and still be quietly dropped into junk where no one looks. There are really three outcomes for any send: it inboxes, it gets spam-foldered, or it bounces and is rejected outright.

This gap is bigger than most senders realize. According to Validity's 2025 benchmark, only around 83% of email reaches the inbox worldwide, which means roughly one in six messages is filtered or lost even when it technically delivered. That missing sixth is invisible in a normal "delivered" report, which is exactly why deliverability is worth understanding rather than assuming. The good news is that almost all of it comes down to a handful of fixable factors, and this guide walks through each one.

Why emails land in spam

Emails land in spam mostly because of who is sending them, not what they say. The single biggest factor is sender reputation, the running score that mailbox providers keep on your sending domain and IP based on how you behave over time. Almost everything else either feeds that reputation or acts as a hard gate in front of it. Here are the main causes, roughly in order of impact:

Notice what is not at the top of that list: spam-trigger words. The idea that certain words drop you in the junk folder is mostly a myth carried over from an older era of filtering. Modern systems are driven by reputation and engagement, so a trustworthy sender can use the word "free" and inbox fine, while a sender with a bad reputation will be filtered no matter how careful the wording. Content still matters a little, covered below, but it is not where the real risk lives.

SPF, DKIM, and DMARC explained

These three are email authentication, and they exist to prove an email is really from who it claims to be. All three are DNS records you publish on your sending domain, which is how mailbox providers verify you and how they tell you apart from someone spoofing your name. They are the price of entry now, so it is worth understanding what each one does.

A little more on each. SPF (Sender Policy Framework) is a public list of approved senders for your domain; a receiver checks whether the server that delivered the message is on it. DKIM (DomainKeys Identified Mail) signs the message with a private key as it leaves, and the receiver uses a public key in your DNS to confirm the signature, which proves both the origin and that nothing was tampered with along the way.

DMARC ties the two together and adds a decision. Its policy can be set to "none" (just monitor and report), "quarantine" (treat failures as suspicious, usually routing them to spam), or "reject" (refuse them outright). DMARC also requires alignment, which simply means the domain in the visible From address has to match the domain that passed SPF or DKIM. That is the part that actually stops spoofing: a scammer can pass authentication on their own domain, but they cannot make it align with yours. A common, safe path is to start DMARC at "none" to watch the reports, then tighten to quarantine or reject once you are sure your real mail is passing.

The Gmail and Yahoo rules

In February 2024, Gmail and Yahoo rolled out shared requirements that turned authentication from a best practice into a requirement. If you send in any volume, these are the rules that decide whether you even get considered for the inbox.

Google defines a bulk sender as anyone sending more than 5,000 messages a day to Gmail accounts, and bulk senders must do three things. First, authenticate with SPF, DKIM, and DMARC, where the DMARC policy is allowed to start at "none." Second, offer a working one-click unsubscribe and a visible unsubscribe link, and honor opt-outs within two days. Third, keep the spam complaint rate low: Google says stay under 0.1% and never reach 0.3%, and Yahoo uses the same 0.3% ceiling. To feel how strict that is, 0.3% is just three complaints per thousand emails.

Even if you are well under the bulk threshold, do not treat these as optional. All senders, at any volume, are expected to have at least SPF or DKIM, valid DNS records, and accurate headers, or risk being rejected or spam-foldered. And the bulk bar is lower than it sounds: a single campaign to a modest list can cross 5,000 Gmail addresses in one send. The simplest reading is to just meet the full bulk requirements from the start, because they are good practice for everyone.

List hygiene and engagement

A clean list is one of the strongest deliverability assets you have, and it starts with permission. Email only people who explicitly opted in, and never buy or scrape addresses, because non-consenting recipients drive complaints and land you on spam traps. Building the list the right way is its own topic, covered in the build an email list guide.

Handle bounces and traps

Bounces come in two kinds. A hard bounce is a permanent failure, like an address that does not exist, and you should remove and suppress it immediately so you never send to it again. A soft bounce is temporary, like a full mailbox, and can be retried, but repeated soft bounces should be treated as hard and dropped. Spam traps are the bigger danger: addresses that exist only to catch senders with poor hygiene. Some are old abandoned addresses recycled into traps, which is exactly why mailing people who went silent years ago is risky. You cannot reliably scrub traps out; you avoid them by only mailing people who opted in and by cleaning your list.

Use a sunset policy

Engagement is now a primary signal, so continuing to email people who never open quietly drags down your reputation for everyone, including the subscribers who do want to hear from you. A sunset policy fixes this: reduce how often you mail someone after a month of no engagement, reduce again after a few months, send one last re-engagement campaign around the six-month mark, and remove anyone who still does not respond. It feels counterintuitive to delete subscribers you worked to get, but a smaller engaged list reaches the inbox far more reliably than a large indifferent one.

Content and warm-up

Two smaller factors round out the picture. Content matters less than reputation, but a few things still hurt, and a brand-new sender has one extra hurdle to clear.

Content that filters notice

The content traps worth avoiding are not really about words. A misleading subject line that does not match the email is both a filtering signal and, in the United States, illegal under the CAN-SPAM Act, which requires the subject and headers to be accurate. Beyond that, watch the basics: an email that is one big image with almost no text reads as spammy, so keep a healthy balance of real text; link to your own authenticated domain rather than bare link shorteners; avoid attachments in bulk mail and link instead; and keep your HTML clean. None of this outweighs reputation, but sloppy content gives a borderline message the final nudge into junk. For the specific case of subject lines, see the email subject lines guide.

Warming up a new sender

Mailbox providers treat a brand-new domain or IP with no reputation almost as warily as one with a bad reputation, so you cannot go from zero to thousands of emails overnight. Warm-up means ramping volume gradually over a few weeks, starting with your most engaged contacts to generate positive signals, and slowing down if complaints or bounces rise. Most small senders never deal with this directly, because they use their email provider's shared sending infrastructure, which already has an established reputation. A dedicated IP, which only makes sense at high volume, must be warmed up by hand, and even a new sending domain on shared infrastructure benefits from a gentle ramp.

How to improve deliverability in 7 steps

Pull it all together into a checklist. Work through these in order and you cover the factors that decide inbox placement.

1. Authenticate your domain with SPF, DKIM, and DMARC

   Publish all three DNS records on your sending domain so providers can verify your mail, starting DMARC at "none" to monitor before you tighten it. Gmail and Yahoo now require all three for bulk senders, so this is step zero, not a nice-to-have.

2. Email only people who opted in

   Build your list with explicit permission, and never buy or scrape addresses. Permission is the foundation of low complaints and trap avoidance, which are the two fastest ways to wreck a sender reputation.

3. Add one-click unsubscribe and honor it fast

   Include a working one-click unsubscribe and a visible unsubscribe link in every marketing email, and process opt-outs within two days. Making it easy to leave keeps complaint rates down, which matters more than holding onto a reluctant subscriber.

4. Keep your list clean

   Remove hard bounces immediately, suppress repeat soft bounces, and apply a sunset policy that drops chronically unengaged subscribers. Mailing dead addresses and old traps is one of the quickest routes to the spam folder.

5. Send content people actually engage with

   Segment and target so opens, clicks, and replies stay high, because engagement is now a primary deliverability signal. Relevant email to a willing audience protects the inbox placement of your whole list.

6. Warm up new domains and ramp volume gradually

   Do not blast a brand-new domain with thousands of emails at once. Start small with your most engaged contacts and raise volume steadily over a few weeks, so providers have time to build trust in you.

7. Monitor your reputation and complaints

   Watch Google Postmaster Tools for your spam rate, reputation, and authentication, track your bounce rate, and check whether you have landed on any blocklists. Catch a slipping metric early, while it is still cheap to fix.

Common mistakes to avoid

Deliverability tends to collapse for the same handful of reasons. Check your sending against this list.

Reach the inbox with systeme.io

Deliverability is one part of email that works together with the rest: see the email marketing guide, and how to build an email list the permission-based way that keeps you out of spam.

Frequently asked questions