Email Deliverability: How to Stay Out of Spam

Why Deliverability Is the Foundation of Email Marketing

You can write the best subject lines, build the most sophisticated automation flows, and have the most engaged subscriber list in your industry, but if your emails land in spam, none of it matters. Deliverability is the invisible foundation that everything else sits on. A store with 95% inbox placement rate and 20% open rate reaches more people than a store with 70% inbox placement and 30% open rate, because the first store has more emails reaching inboxes to begin with.

The major email providers, Gmail, Yahoo, Outlook, and Apple Mail, use increasingly sophisticated algorithms to decide which emails reach the inbox, which go to the promotions tab, and which get filtered to spam. These algorithms consider your domain authentication, sender reputation, subscriber engagement history, email content, and sending patterns. Getting any of these wrong can tank your inbox placement virtually overnight.

Since February 2024, Google and Yahoo enforce stricter sender requirements for anyone sending over 5,000 emails per day. Senders must authenticate with SPF, DKIM, and DMARC, maintain spam complaint rates below 0.3%, include easy one-click unsubscribe headers, and honor unsubscribe requests within 2 days. Failing to meet these requirements results in emails being blocked or sent to spam.

DNS Authentication: SPF, DKIM, and DMARC

Email authentication uses DNS records to verify that emails claiming to come from your domain are actually authorized by you. Without these records, any spammer can send emails that appear to come from yourdomain.com, and email providers have no way to distinguish legitimate messages from spoofed ones. Setting up authentication is the single most important deliverability action you can take.

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses and services are authorized to send email on behalf of your domain. When you use Klaviyo or Mailchimp to send emails from your domain, your SPF record needs to include their sending servers. The record is a TXT entry in your domain's DNS that looks like "v=spf1 include:_spf.google.com include:spf.klaviyo.com ~all" where each "include" authorizes a sending service. Your email platform provides the exact include value to add.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to every email you send, proving the message was not altered in transit. Your email platform generates a public/private key pair. The private key signs outgoing emails, and the public key is published as a DNS record so receiving servers can verify the signature. DKIM setup involves adding one or two CNAME or TXT records to your DNS, with the exact records provided by your email platform.

DMARC (Domain-based Message Authentication, Reporting and Conformance)

DMARC tells receiving servers what to do with emails that fail SPF or DKIM checks. Without DMARC, a failed check might still deliver the email. With DMARC, you can instruct servers to quarantine (send to spam) or reject (block entirely) unauthorized emails. Start with a monitoring-only policy "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com" that reports failures without taking action. After reviewing reports for 2 to 4 weeks and confirming all legitimate senders pass authentication, upgrade to "p=quarantine" and eventually "p=reject."

Setting up all three records typically takes 15 to 30 minutes if you have access to your domain's DNS settings. Every major email marketing platform provides step-by-step instructions specific to common DNS providers like Cloudflare, GoDaddy, and Namecheap. Verify your setup using free tools like Google's Check MX or mail-tester.com.

Building and Maintaining Sender Reputation

Your sender reputation is a score that email providers assign to your sending domain and IP address based on how recipients interact with your emails. High engagement (opens, clicks, replies) builds positive reputation. Low engagement (ignores), spam complaints, and bounces build negative reputation. This score directly determines whether your emails reach the inbox or get filtered.

Engagement signals. Gmail and other providers track whether recipients open your emails, click links, reply, move emails from spam to inbox (very positive), add your address to contacts (positive), mark as spam (very negative), or consistently ignore your messages without unsubscribing (negative). The implication is clear: sending emails only to people who want them is not just good practice, it is a deliverability requirement.

Bounce management. Hard bounces (email address does not exist) should be removed from your list immediately after the first bounce. Most email platforms handle this automatically. Soft bounces (temporary issue like full mailbox) should be retried a few times, then suppressed if they persist. A bounce rate above 2% on any send signals list quality problems to email providers. Clean your list regularly by removing addresses that have bounced.

Spam complaints. When a subscriber clicks the "Mark as Spam" button in their email client, your sender reputation takes a direct hit. Google and Yahoo require bulk senders to maintain spam complaint rates below 0.3%, meaning fewer than 3 complaints per 1,000 emails sent. The best way to keep complaints low is to only send to subscribers who opted in, make unsubscribing easy and instant (so they unsubscribe instead of clicking spam), and segment your list so content stays relevant.

Warming Up a New Sending Domain

If you are starting email marketing for the first time, switching email platforms, or sending from a new domain, you need to warm up your sender reputation gradually. Sending 10,000 emails on day one from a domain with no sending history is a spam signal because that is exactly what spammers do when they acquire new domains.

A proper warm-up schedule looks like this: Week 1, send to your 200 to 500 most engaged subscribers (recent openers and clickers). Week 2, expand to 1,000 to 2,000 subscribers. Week 3, expand to 5,000 subscribers. Week 4 and beyond, send to your full list. During warm-up, send your best content to encourage high engagement rates, which builds a positive reputation faster.

If you are migrating from one email platform to another, the warm-up is still necessary because the new platform uses different sending infrastructure. Your previous sender reputation does not transfer. Some platforms like Klaviyo offer shared IP pools for smaller senders that already have some reputation built in, which reduces warm-up time. Larger senders on dedicated IPs need to warm up more carefully.

List Hygiene Practices

Regular list cleaning is one of the most effective deliverability practices, yet most stores neglect it because removing subscribers feels counterproductive. In reality, removing disengaged subscribers improves deliverability for the engaged ones, often resulting in higher total revenue despite the smaller list.

Sunset flow. Create a re-engagement sequence that targets subscribers who have not opened or clicked any email in 90 days. Send 2 to 3 emails asking if they still want to hear from you, with increasingly direct language. If they do not engage with any re-engagement email, suppress them from all future sending. Run this flow continuously so disengaged subscribers are cleaned automatically.

Regular purges. Every quarter, review your list for subscribers who have been suppressed, have hard bounced, or have not engaged in 120 or more days despite re-engagement attempts. Remove them permanently. This keeps your list accurate and your engagement metrics representative of your actual active audience.

Email verification. When importing contacts from another system or collecting emails through forms without double opt-in, run the list through an email verification service like ZeroBounce, NeverBounce, or BriteVerify. These services identify invalid, temporary, and spam-trap email addresses before you send to them. The cost of verification ($3 to $10 per 1,000 addresses) is trivial compared to the deliverability damage from sending to bad addresses.

Monitoring Your Deliverability

Track inbox placement rate separately from open rate. Open rate tells you how many delivered emails were opened. Inbox placement rate tells you how many sent emails actually made it to the inbox (versus spam or blocked). Tools like GlockApps, Mail-tester.com, and Litmus test inbox placement across multiple email providers.

Watch for sudden drops in open rates, which often indicate a deliverability problem rather than a content problem. If your open rate drops from 22% to 12% overnight, check your bounce rate, spam complaint rate, and authentication status before assuming your subject lines are the issue. Most email platforms surface these metrics in their analytics dashboards.

Google offers Postmaster Tools, a free service that shows your domain reputation, spam rate, authentication results, and feedback loop data for emails sent to Gmail addresses. Since Gmail represents 30% to 40% of most consumer email lists, monitoring your Gmail reputation is critical. Set up Postmaster Tools and check it weekly to catch reputation issues early.