You can have a 98% delivery rate and still have half your emails sitting in spam folders. Delivery means the server accepted your message. Deliverability means someone actually sees it.

This guide covers why emails land in spam, how to check your current deliverability, and the specific steps that keep your outbound hitting the inbox at scale.

Email deliverability is whether your emails land in the recipient’s inbox or get filtered into spam. To improve it, focus on three areas: authenticating your domain, cleaning your mailing list, and maximizing recipient engagement.

Here’s a distinction worth knowing early: delivery and deliverability are different things. Delivery means the recipient’s server accepted your email. Deliverability means that email actually showed up in the inbox where someone will see it. You can have 99% delivery and still have half your emails sitting in spam folders, invisible to the people you’re trying to reach.

Mailbox providers like Gmail and Outlook run algorithms that decide where each email goes. Before jumping into fixes, it helps to understand what triggers spam placement in the first place.

Sender reputation is a trust score that mailbox providers assign to your domain and IP address. The score builds over time based on how recipients interact with your emails. When people ignore, delete, or mark your messages as spam, your reputation drops. Once it drops, future emails are more likely to be filtered, even if the content is fine.

Unauthenticated emails look suspicious to providers because there’s no proof you’re the legitimate sender. Three protocols handle authentication: SPF, DKIM, and DMARC. Without them, providers have no way to verify that an email claiming to be from your domain actually came from you. We’ll cover how to set up authentication in the best practices section below.

Certain words and formatting patterns signal spam to filters. Common triggers include:

Hard bounces happen when you send to addresses that don’t exist. Soft bounces are temporary issues, like a full inbox. Both hurt your reputation, though hard bounces are worse because they indicate you’re sending to unverified lists.

Spam complaints occur when recipients click “Report Spam” on your email. Even a small number of complaints signals to providers that people don’t want your messages, and providers respond by filtering more aggressively.

Providers watch for sudden jumps in sending volume. If a new or dormant domain starts sending hundreds of emails overnight, that pattern looks like spammer behavior. Gradual increases over time appear more legitimate because real businesses don’t typically go from zero to hundreds of emails in a day.

Inbox placement rate measures the percentage of emails that land in the primary inbox rather than spam or promotions tabs. For cold outbound, aim for inbox placement above 90%.

Inbox placement rate differs from delivery rate. Delivery rate only tracks whether the server accepted the email. A 98% delivery rate with 60% inbox placement means nearly 40% of your emails are going to spam, even though they were technically “delivered.” When evaluating your performance, inbox placement is the metric that actually matters.

Before fixing problems, you want to know where you stand. A few methods give you visibility into your current deliverability:

lemlist’s Deliverability Hub centralizes all of this, so you can monitor mailbox health, spot issues early, and get actionable recommendations in one place.

The following steps address the root causes of spam placement. Work through them in order, since authentication and warmup form the foundation for everything else.

Authentication proves to mailbox providers that you’re the legitimate sender. Each protocol handles a different piece of verification:

Setting up authentication requires adding DNS records to your domain. lemlist automates this configuration, so you can connect a domain and have authentication handled without manual DNS editing.

Warmup is the process of gradually increasing your sending volume to build trust with mailbox providers. A brand new domain sending 500 emails on day one looks suspicious. The same domain sending 10 emails on day one, 20 on day five, and scaling up over several weeks looks normal.

During warmup, you want real engagement: opens, replies, and emails moved out of spam. lemwarm automates this by exchanging real emails with real inboxes at a controlled pace, building your sender reputation without manual effort. The process typically takes two to four weeks depending on your target daily volume.

Never send cold emails from your primary company domain. If deliverability issues occur, you want them isolated to a sending domain rather than affecting your main domain’s reputation.

For example, if your company domain is acme.com, create a separate domain like outreach-acme.com or getacme.com for cold outreach. This protects your primary domain while giving you flexibility to test and scale without risk.

Sending to invalid addresses increases your bounce rate, which damages sender reputation. Email verification checks whether an address exists and can receive mail before you send.

lemlist provides verified contact data from top data providers, so you can build lists with confidence that the addresses are real. You can also verify addresses you’ve collected elsewhere before adding them to campaigns.

Each mailbox has safe daily limits based on its age and reputation. Exceeding those limits triggers provider throttling or spam filtering.

A common approach is spreading volume across multiple mailboxes. Instead of sending 200 emails from one inbox, send 50 each from four inboxes. lemlist enforces automatic sending caps to keep each mailbox within safe ranges, so you don’t accidentally burn a mailbox by sending too much too fast.

Emails sent from Gmail to Gmail or Outlook to Outlook often have better inbox placement than cross-provider sends. This is called provider matching, and it works because same-provider routing tends to be trusted more by the receiving server.

lemlist routes emails automatically based on the recipient’s provider, so your Gmail mailboxes send to Gmail recipients and your Outlook mailboxes send to Outlook recipients without manual sorting.

Subject lines are the first thing spam filters evaluate. A few patterns help avoid triggering filters:

The goal is to write subject lines that sound like a real person wrote them for a specific recipient, because that’s exactly what spam filters are trying to detect.

Generic templates perform worse than personalized messages because recipients engage less. Low engagement (few opens, no replies) signals to providers that your emails aren’t wanted, which hurts future deliverability.

Personalization based on real data points, like recent LinkedIn activity, company news, or hiring signals, increases the chance of a reply. lemlist’s data enrichment agents pull structured insights from LinkedIn, websites, and other sources so you can tailor each message to something specific about the recipient.

Tracking the right metrics helps you catch problems before they compound. Here’s what to watch:

lemlist surfaces all of this with alerts, so you can act quickly when something shifts rather than discovering problems weeks later.

Google and Yahoo have published requirements for bulk senders that affect deliverability. The key mandates include proper authentication (SPF, DKIM, DMARC), easy one-click unsubscribe, and keeping spam complaint rates low. Review Google’s and Yahoo’s official documentation for current specifics, since requirements can change.

If your emails are already landing in spam, recovery is possible but takes time. The process follows a sequence:

lemlist’s mailbox-level tech audits identify specific issues, like failing DKIM signatures or DNS misconfigurations, so you know exactly what to fix rather than guessing.

lemlist combines domain setup, warmup (lemwarm), sending controls, and monitoring in one platform. The Deliverability Hub gives you visibility into mailbox health and actionable fixes without requiring technical expertise.

You can connect an existing domain or purchase a new sending domain directly in lemlist, with authentication configured automatically. From there, warmup, volume caps, provider matching, and ongoing monitoring work together to protect your sender reputation as you scale.

Warmup typically takes two to four weeks of gradually increasing volume. The exact timeline depends on your target daily send rate and how quickly you build positive engagement signals like opens and replies.

Yes. Most outbound teams use shared IPs successfully. Authentication, sending practices, and list quality matter more than IP type for cold email deliverability.

Safe limits vary by mailbox age and reputation. Start with 20–50 emails per day for new mailboxes and increase gradually while monitoring bounce and complaint rates.

Purchased lists contain unverified and unengaged contacts. Sending to them leads to high bounces and complaints, which damage your sender reputation quickly.

Use blocklist lookup tools like MXToolbox or check Google Postmaster Tools for reputation warnings. lemlist’s Deliverability Hub also surfaces blocklist issues so you can address them before they affect your campaigns.