Most solo operators watch open rates like a hawk. A 40% open rate feels like success. A 25% rate triggers panic and a subject-line audit.
But open rate measures engagement among people who received your email in their inbox. It tells you nothing about the readers who never saw it because Gmail, Outlook, or Apple Mail dumped it straight into spam or the Promotions tab.
If 30% of your list never sees your email, a 40% open rate on the remaining 70% means your true reach is closer to 28%. You’re optimising the wrong number.
What deliverability actually measures
Deliverability isn’t whether your ESP successfully handed off the email to the recipient’s server. That’s the delivery rate, and it’s usually above 98% unless your domain is blacklisted.
Deliverability is inbox placement—the percentage of delivered emails that land in the primary inbox, not spam, not Promotions, not the Updates tab.
Your ESP’s dashboard won’t show this number by default. Most platforms report delivery rate and open rate, then stop. A 99% delivery rate and 35% open rate looks healthy until you discover that 40% of your delivered emails went straight to spam.
How to check where your emails actually land
The simplest method: seed lists. Create a free account on Gmail, Outlook, Yahoo, and Apple iCloud. Add those addresses to a hidden segment in your ESP. Send every broadcast or automation to that segment, then manually check each inbox and spam folder within an hour of sending.
Log what you see:
- Primary inbox
- Promotions tab (Gmail)
- Spam folder
- Not delivered at all
Do this for ten consecutive sends. If more than two land in spam or Promotions, you have a placement problem, not an engagement problem.
For a more automated approach, use a tool like GlockApps, Mail-Tester, or Litmus Spam Testing. These services give you test addresses across dozens of providers and return placement reports within minutes. GlockApps starts at $49/month for 30 tests. Mail-Tester offers pay-as-you-go at $0.50 per test. Litmus Spam Testing is included in Litmus Email Analytics plans starting at $99/month.
What breaks inbox placement (and what doesn’t)
Common advice blames spammy subject lines or too many exclamation points. In practice, inbox placement breaks for infrastructure reasons first, content reasons second.
Authentication failures. If your SPF, DKIM, or DMARC records are misconfigured or missing, ISPs treat your emails as unverified. Even a single failed authentication check can trigger spam filtering. Check your DNS records using MXToolbox or dmarcian. If you’re sending from a subdomain (e.g., news.yourdomain.com), make sure your DKIM selector matches and your SPF record includes your ESP’s sending IPs.
Low engagement history. ISPs track how recipients interact with your domain over time. If your last ten emails had sub-20% open rates or high spam-complaint rates, future emails start in spam by default. This creates a vicious cycle: spam placement lowers engagement, which worsens future placement.
Sudden volume spikes. Sending to 5,000 subscribers after months of sending to 500 looks like a compromised account. Ramp slowly. If you’re reactivating a cold list or migrating ESPs, warm your domain by sending to your most engaged segment first, then expand over two weeks.
Shared IP reputation. If you’re on a shared sending IP (most ESPs below $100/month), your placement depends partly on other senders using the same IP. One spammer on your IP can hurt your placement. Platforms like Postmark and Mailgun isolate transactional senders onto separate IP pools with stricter quality controls. If you’re sending fewer than 50,000 emails per month, a shared IP on a quality ESP is usually fine—just avoid the cheapest bulk-email platforms.
The non-obvious fix: prune faster
Here’s the tactic most operators resist: remove unengaged subscribers before they hurt your sender reputation.
If someone hasn’t opened an email in 90 days, they’re either not reading, using an email client that blocks tracking pixels, or your emails are landing in spam. Keeping them on the list lowers your engagement rate, which signals to ISPs that your content isn’t wanted.
Set up a 90-day re-engagement automation: one plain-text email asking if they still want to hear from you, with a clear unsubscribe link. If they don’t click within seven days, remove them from your main list. Move them to a separate “cold” segment if you want to try again in six months, but stop sending regular broadcasts.
This will drop your subscriber count. It will improve your open rate, click rate, and inbox placement. ISPs reward senders who mail engaged audiences.
One metric to watch weekly
If you track one number, make it your spam complaint rate—the percentage of recipients who mark your email as spam. Your ESP’s dashboard will show this, often buried under “Abuse Reports” or “Complaints.”
Anything above 0.1% (one complaint per 1,000 emails) is a red flag. Above 0.3%, ISPs start throttling your delivery. Above 0.5%, you’re headed for blacklist territory.
If your complaint rate spikes, stop sending and audit your signup flow. Are people actually opting in, or are you adding them without explicit consent? Is your unsubscribe link visible and one-click? Are you sending more frequently than you promised at signup?
Most complaint spikes trace back to expectation mismatches, not content quality.
Want to go deeper on email infrastructure and deliverability tactics? Reply to this email with your biggest placement headache—I’ll cover the most common issues in a future piece.