Rémi Kokabi | Updated August 10, 2026 | 17 min read

How to improve email deliverability and stay out of spam

How to improve email deliverability and stay out of spam

By Grégoire | June 24, 2025 | 23 min read
Let me tell you a quick story.
I was once convinced I had written the perfect cold email. Great subject line, killer opening, strong CTA, and a clear value prop. The whole package.
Open rate? 21%.
Why? Because it never made it to the inbox.
The hard truth is: you can write the best email in the world, but if it ends up in spam, it might as well not exist.
In this guide, I’ll show you how I send 100,000+ cold emails a year without getting flagged or ignored.
This is a practical, step-by-step playbook on how to improve email deliverability.
It’s packed with tactics, tech tips, and tools that work.
You’ll find everything you need to keep your emails in the inbox.

Why a 97% delivery rate can still mean poor ROI

First things first: let’s clear up a common confusion.
  • Email delivery means your email was accepted by the server.
  • Email deliverability means it landed in the inbox (not spam, promotions, or updates).
You can have a 97% delivery rate and still lose money because your emails don’t get seen.
Validity’s 2026 Email Deliverability Benchmark Report found the global average inbox placement rate reached 87.2% in 2025, a 3.7 percentage-point improvement over 2024 (when it was 83.5%). The Software/SaaS sector lagged the global average at 80.9% in 2024, one of the lower-performing commercial sectors.
That’s still roughly 13% of your efforts, budget, and time going to waste.
If your deliverability is off, every other email metric suffers. Open rate, reply rate, and conversion all drop.
So how do you improve email deliverability?

The tactics that improved my email deliverability

Deliverability isn’t just about one setting or one tool. It’s a system that ties together your technical setup, sending patterns, list hygiene, email content, and real-time monitoring. lemlist’s Deliverability Hub handles inbox rotation, volume caps, time-zone-aware sending, a pre-send Deliverability Boost, and list verification in one place, so you’re not stitching together manual workflows.

Step 1: Nail your technical setup (meet SPF, DKIM, and DMARC)

Before anything else, get this part right to improve email deliverability. Your cold email campaign could be perfectly written, well-targeted, and timed. But if your domain isn’t authenticated, you’re not even playing the game. Internet service providers (ISPs) use authentication protocols to verify that you are who you say you are. If you don’t have them properly configured, your emails will be treated as suspicious.
Quick comparison of what each protocol does:
  • SPF: declares which servers can send emails for your domain and blocks spammers from impersonating you.
  • DKIM: signs your messages to verify they weren’t altered in transit, proving your content is legit.
  • DMARC: tells inboxes what to do if SPF or DKIM fails, sends reports, and gives you control plus visibility.
SPF (Sender Policy Framework) Think of SPF as your “approved sender list.” When your email hits a server, the recipient checks your domain’s SPF record to verify the sending IP is legit. Example SPF record: v=spf1 include:_spf.google.com ~all. Steps: 1) Log into your DNS settings. 2) Add a new TXT record. 3) Paste the correct SPF value (use only the services you actually send from). 4) Test your record using lemlist’s SPF checker. 5) Save and propagate changes. Avoid this common mistake: too many include: directives can cause SPF to fail (DNS lookup limit is 10). Here’s a more comprehensive guide on how to create an SPF record.
DKIM (DomainKeys Identified Mail) DKIM is like sealing your email with a wax stamp. It proves the message hasn’t been altered in transit. Your ESP (like Google Workspace) uses a private key to sign each outgoing email. The recipient uses your public key (in DNS) to check the signature. What to do: 1) Enable DKIM in your email provider’s admin panel. 2) Add the generated TXT record to your DNS (it’ll look something like google._domainkey.yourdomain.com). 3) Once it’s in place, your emails will be signed automatically. Pro tip: don’t skip this just because you’re “not technical.” Here’s a more comprehensive, up-to-date guide on how to set-up your DKIM for your domain.
DMARC (Domain-based Message Authentication, Reporting & Conformance) DMARC ties SPF and DKIM together and tells inboxes how to handle failures. It’s also the only protocol that gives you visibility through aggregated reports. Start with a soft policy: v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com. Then move to p=quarantine to send failures to spam, and p=reject to block them completely. Steps: 1) Create a DMARC record as a TXT entry in your DNS. 2) Use the format above, swapping in your own reporting address. 3) Monitor reports for a few weeks before tightening your policy. Run a free DMARC check here.
If you skip these three protocols, your emails are more likely to land in spam, spammers can spoof your domain, and you’ll have zero visibility into who’s impersonating you.
With lemlist, you can connect an existing domain in seconds or purchase a new sending domain directly in-app, and automated deliverability setup configures your authentication records automatically. No manual DNS work required.

Step 2: Warm up your inboxes

Don’t skip this step, even if you’re a pro. Whether you’re launching a new outbound campaign or just added a fresh inbox, warming up is non-negotiable if you care about sender reputation and improving email deliverability.
Your sender reputation is your email credit score. If inbox providers trust you, you improve email deliverability and get inbox placement. Your sender reputation is built over time and shaped by consistent sending patterns, bounce rates, spam complaints, open and reply rates, blocklists, and domain age.
How I warm up every inbox: Day 1, send 5 emails; ramp up volume by 2 emails/day until you reach 50. Validity calls warmup “a fundamental part of helping a sender build trust and increase the likelihood of your emails being delivered to subscribers’ inboxes,” noting that most senders need a month or longer before reaching their target volume. Bonus: with lemwarm, inbox warm-up is automated. lemwarm sends emails to real inboxes in the network, simulates real replies and engagement, and adjusts volume over time to build trust. If you’re running bulk sends from a dedicated SMTP, warm up that IP the same way you would a domain.
Pro tip on domain reputation: stick to a predictable daily volume, send to highly engaged leads first, avoid cold starts and random spikes, monitor reply rates (not just open rates), and don’t send newsletters and cold emails from the same domain.
How I keep my sender score above 90 (and off blacklists): Instead of checking each tool by hand, deliverability monitoring and alerts in lemlist consolidates warmup health, bounce trends, and inbox-placement tests with automated alerts when something goes off track. For additional context, I also review Google Postmaster Tools for reputation trends and spam complaints, Microsoft SNDS for behavior with Outlook, and Spamhaus and Barracuda to confirm I’m not blacklisted. lemlist’s Deliverability Setup Checker offers instant validation of SPF, DKIM, DMARC, and domain health. A drop in sender score is usually a sign of a deeper deliverability issue.

Step 3: Clean your lists (before every campaign)

You can do everything else right, but if your list hygiene is off, you’re doomed to bounce. Every email you send to an invalid or unengaged address increases the chances of landing in spam. ISPs track it.
Why list hygiene equals inbox placement: when providers see you consistently sending to valid, engaged users, you’re a trusted sender; invalid or silent users look like suspicious activity. If you’re not cleaning your list monthly, you’re already behind.
Bounce rate guide: under 3% is good; 2-4% is ok (monitor and clean soon); 4-6% careful (immediate cleaning needed); over 6% stop (fix issues). You can track your bounce rate on lemlist in your campaign statistics.
How I clean my lists: use email verification before every campaign; remove hard bounces immediately; remove soft bounces after 3 failed attempts; re-engage or sunset contacts inactive for 60+ days. Hard bounce = address doesn’t exist (remove immediately). Soft bounce = temporary issue (remove after 3 attempts). Inactive = no opens or clicks in 60+ days (start re-engagement or sunset).
The 6-month rule is too generous. Instead, I follow a 60-day sunset policy: after 60 days of inactivity, send a re-engagement email; if no response, remove from primary list; optionally add to a dormant segment.
Use double opt-in to build a list with higher engagement. Double opt-in means your contact confirms their subscription twice: once by submitting a form, and again by clicking a confirmation email. Compared with single opt-in, it means higher engagement quality, much lower risk of bounces and spam complaints, and stronger GDPR/CAN-SPAM safety.
An instant way to kill your deliverability: purchased lists. You don’t know the source, there’s a high chance of invalid or fake addresses, you’ll hit spam traps and blacklists, and it’s usually not GDPR, CAN-SPAM, or CCPA compliant. It’s risky and usually illegal. On lemlist, we focus on verified leads from clean data, enriched ethically, and validated before sending.
Create these segments to avoid spam filters: behavior-based (clicked vs. opened only vs. no activity), persona-based (title, industry, location), email source (cold, warm, inbound form, referral, webinar signup), recently engaged (last 7 days, 30 days, 90 days), and inactive (45+ days, 60+ days).

Step 4: Write cold emails that don’t land in spam, at scale

Even with perfect technical setup, bad copy can get you flagged. Spam filters analyze your subject line, your word choices, your tone, and how predictable your emails are.
Why email content still gets you spam-filtered: modern spam filters are powered by AI, engagement history, and pattern detection. Using a known spam phrase can get you flagged; sending the same email to 100 people can trigger filters; even good emails with bad formatting can get routed to promotions or spam.
The words that send your email straight to spam (avoid these especially in subject lines and CTAs): “Act now!”, “Free trial”, “Double your income”, “Earn $$$ from home”, “Risk-free”, “Buy now / Click here”, “Guaranteed”. Formatting red flags: ALL CAPS SUBJECTS, excessive punctuation, emojis in subject lines. What I do instead: keep subject lines short (under 3 words), keep tone casual and confident, write like I’m starting a real conversation.
Keep it plain text. The simpler the email, the better your chances of reaching the inbox: no images in cold emails, no hyperlinks unless part of a reply CTA (and even then I test), use clean HTML, keep text-to-image ratio at 80/20 or better, and always include a plain text version if you’re sending multi-part emails. On lemlist, “plain text” mode is one click in the campaign editor.
Personalize with context that’s specific to each lead. Dropping “Hi {firstName}” into a template reads as automation, so earn the reply with real signals. What works: referencing their job title, mentioning a recent product launch or hiring round, commenting on a pain point they’re likely facing, using dynamic content that changes per industry or company size. I use liquid syntax to vary structure and keep each message unique, which makes campaigns harder for spam filters to detect as mass outreach.
How I use AI to scale without triggering spam filters: on lemlist, I use AI-powered icebreakers to change phrasing from lead to lead, vary sentence structures, and add behavioral relevance (company growth, funding, role-specific pain). This reduces repeat patterns and makes the copy feel human. Need inspiration? Check our prompts library.
Add a one-click unsubscribe in the footer. Inbox providers like Gmail and Yahoo now require a one-click unsubscribe for bulk senders. It reduces spam complaints, improves your sender reputation, and makes your emails look more trustworthy. Add a clear “unsubscribe” link in the footer, avoid link shorteners, and don’t hide it behind vague wording.

Step 5: Send the right volume with inbox rotation

ISPs monitor volume, frequency, and consistency. My golden rule: never send more than 30-50 cold emails per inbox per day.
How I structure inbox rotation to send 500+ emails/day: inbox rotation spreads sending volume across multiple domains and inboxes, so no single identity gets burned. For 500 emails/day, I use 3-4 domains, 2-3 inboxes per domain, and rotation logic to spread volume evenly. This protects your sender reputation, lets you pause compromised inboxes, and ensures stable, predictable volume per sender. More on inbox rotation here.
Send with strategy, not speed: rotate across 6-10 inboxes rather than sending 200 from one; spread sends over 2-4 hours rather than blasting all at once; increase volume gradually (~10% per week) rather than doubling overnight; prioritize recently active leads; personalize using liquid syntax or AI rather than reusing one subject line for 300 emails.
Test different sending times to see what gets opened: morning (8-10 AM), midday (12-2 PM), end-of-day (4-6 PM). Run A/B tests over 1-2 weeks per segment. Don’t send mass blasts at the same second. With lemlist, you can set different campaign schedules to manage email volumes.

Email deliverability techniques most senders miss

Most people stop at SPF and subject lines. To consistently reach the inbox at scale, you need to go beyond the basics.
Use dedicated IPs only when sending 100,000+ emails/month. Dedicated IPs suit high-volume transactional and marketing email, where the sender can keep the pace those IPs need. Shared IP: easy setup, warmed reputation, but you share risk (best for startups and low-volume senders). Dedicated IP: full control and exclusive reputation, but needs manual warm-up and consistent volume (best for high-volume campaigns). If you’re not sending at least 100,000 emails/month, stick with a trusted shared IP. If you go dedicated, follow strict warm-up protocols and use lemlist’s Deliverability Setup Checker to track your IP’s health across blacklists and ISP reputation.
Test your emails across top clients to prevent rendering issues. Your email could look fine in Gmail but break in Outlook or Apple Mail. Broken layouts mean poor experience, lower engagement, and more spam filtering. Before I launch a sequence, I test on Gmail (desktop + mobile), Outlook, Apple Mail, Yahoo, and iOS/Android default apps. Tools: lemlist (preview for recipients on desktop + mobile), Litmus, Email on Acid.
Verify inbox placement using pre-send tests (not just delivery rates). Just because your email was “delivered” doesn’t mean it reached the inbox. Inbox placement testing shows where your email lands: primary inbox, promotions tab, spam, or blocked. With lemlist, you can run inbox placement tests across Gmail, Microsoft, and other providers to see where emails land before campaigns go live. The Deliverability Boost component also pre-checks campaigns for risky content, technical misconfigurations, and inbox placement signals so you can fix issues before sending.

Adapt your email strategy to work with AI-based filtering systems

Spam filters used to be keyword-based. Today they’re trained by AI models that adapt in real time to how your recipients engage with your emails.
AI filters track historical engagement, not just keywords. Email providers like Gmail and Outlook use AI and machine learning to evaluate your sending behavior over time. Low open/reply rates over time are a negative signal; manual deletions or no responses get flagged as low engagement; consistent engagement (opens, replies, forwarding, clicks) builds inbox trust. Every send impacts future inbox placement, and your past performance becomes your reputation. Focus on high-quality leads, smart segmentation, personalization that earns opens and replies, and pruning inactive contacts regularly.
lemlist’s Deliverability Hub helps you stay ahead of these filters. The Deliverability Boost runs pre-send checks to surface risky content and configuration gaps, while Monitoring & Alerts tracks inbox-vs-spam ratios per mailbox, provider, and domain so you can catch reputation damage early.

The elements in every email to stay GDPR, CAN-SPAM, and CCPA compliant

  1. Consent: you must have a legal basis to email someone (opt-in, legitimate interest, or business relationship), especially strict under GDPR and CCPA.
  2. Identification: always state who you are (sender name + organization) and use a real reply-to address.
  3. Physical address: include your company’s valid physical mailing address in the footer (required by CAN-SPAM and GDPR).
  4. Easy opt-out: offer a clear, one-click unsubscribe that’s easy to find (required under Gmail and Yahoo’s 2024 sender requirements).

Essential tools to monitor and fix email deliverability issues

Authentication checkers: 1) lemlist Deliverability Setup Checker instantly validates SPF, DKIM, and DMARC, plus blacklist status. 2) MXToolbox offers deeper DNS diagnostics and DMARC formatting.
Spam and content testers: 3) lemlist’s Spam Checker shows a 0-10 score based on copy, formatting, links, and structure. 4) Mail-Tester offers quick spam-score checks using a generated email address.
Blacklist monitoring: 5) Talos Intelligence (Cisco) checks whether your domain or IP has been flagged. 6) Spamhaus and Barracuda are widely used spam databases.
Sender reputation and inbox health: 7) Gmail Postmaster Tools tracks domain reputation, spam complaints, and delivery errors. 8) Microsoft SNDS is the Outlook equivalent. If you run multiple domains, build a weekly dashboard tracking sender score, bounce rates, blacklist status, and open rates side by side.
For a single-pane view that consolidates warmup health, bounce trends, delivery rates, and inbox-placement signals across all your mailboxes, lemlist’s Deliverability Hub pulls everything into one dashboard with automated alerts when something goes off track.

My checklist when emails suddenly land in spam

  1. Check SPF, DKIM, and DMARC with lemlist’s setup checker.
  2. Review your latest content (subject lines, links, spam terms).
  3. Check for recent blacklistings (Talos, MXToolbox, Spamhaus).
  4. Look at your bounce rate: if over 2%, stop sending and revalidate your list using ZeroBounce or Bouncer.
  5. Assess sending volume: did you spike without warming up? If more than 2 of these look off, pause the campaign, fix, and test before resuming.

Deliverability is something you earn over time

Email deliverability is a continuous process. You’re building a reputation every day, with every message, every bounce, and every unsubscribe.
To stay in the inbox: nail your technical setup, warm up new domains and inboxes, clean your lists consistently, write content that feels human, respect privacy laws, and monitor your setup weekly.
Stop chasing hacks. Deliver consistent value and build real relationships. Teams rate lemlist 4.6/5 from 2,000+ reviews on G2 because it makes protecting deliverability practical at scale.
Still not sure what’s holding you back? Run a deliverability test or See how the Deliverability Hub works.
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FAQ

How can I boost my email deliverability quickly? Start by fixing your technical setup (SPF, DKIM, DMARC), validating your list, and stopping any campaign with a bounce rate over 2%. Keep sending volume low and consistent while you rebuild reputation.
Does DKIM really improve email deliverability? Yes. DKIM is one of the key signals inbox providers use to verify message authenticity. Without it, even great emails can land in spam.
What is a good sender score for email deliverability? A sender score above 90 is excellent. Between 70-89 is acceptable. Below 70 needs immediate investigation. Use tools like Google Postmaster Tools and Talos Intelligence to track.
How do I perform an email deliverability test effectively? Use lemlist’s deliverability test tool or Mail-Tester. Send to multiple inbox types (Gmail, Outlook, Yahoo), monitor placement, and review SPF/DKIM/DMARC configuration.
Why are my emails from HubSpot / Klaviyo going to spam? Mass platforms often use shared IPs. If your authentication isn’t set up, or if your list has unengaged contacts, your emails can be filtered, especially by Gmail. Check SPF/DKIM/DMARC and sender reputation.
What’s the difference between email delivery and email deliverability? Delivery means the message was accepted by the receiving server. Deliverability means the message actually landed in the inbox (not spam, promotions, or updates).
How does BIMI relate to email deliverability? BIMI lets you display your logo in supported inboxes. While it’s not a ranking factor, it enhances trust, which can lead to higher engagement and better placement.
Can I get help with deliverability? Yes. lemlist’s Deliverability Hub gives you automated setup, warmup, inbox rotation, and monitoring in one place. For hands-on guidance, you can book a demo and walk through your setup with our team.
By Grégoire Luel, Lead Account Executive @lemlist.
RémiRémi Kokabi
Hi there, I’m Rémi, co-founder of the GTM Club powered by lemlist & Claap. If you believe Go-To-Market is the new moat in this AI-era, you should apply: https://www.thegtmclub.com/
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