Why Deliverability is Everything
You can write the perfect cold email. You can have the best offer in your market. None of it matters if your emails land in spam.
The hard truth is that most cold emailers have deliverability problems they don’t even know about. They’re sending into the void, wondering why reply rates are under 1%. They’re crafting personalized messages, researching prospects, testing subject lines—all while their emails never even make it to the inbox.
Here’s what good deliverability looks like: you should be hitting 95% or higher inbox placement rate, keeping your bounce rate under 2%, maintaining spam complaints below 0.1%, and seeing consistent open rates above 40%. If you’re not hitting these numbers, you’re leaving money on the table. This guide will fix that.
The Three Pillars of Cold Email Deliverability
After helping dozens of companies set up their cold email infrastructure, we’ve learned that deliverability comes down to three fundamental pillars. Authentication proves you’re allowed to send from your domain. Reputation builds trust with email providers over time. And content ensures you’re writing emails that don’t trigger spam filters.
Miss any one of these, and you’re fighting an uphill battle. Get all three right, and you’ll consistently land in the inbox. Let’s break each one down.
Pillar 1: Email Authentication
Think of authentication as your email’s passport. It tells email providers “yes, this person is authorized to send from this domain.” Without it, you’re basically anonymous—and anonymous senders go to spam.
There are three authentication protocols you need to set up: SPF, DKIM, and DMARC. Each serves a different purpose, and you need all three working together.
SPF: Your Authorized Sender List
SPF, or Sender Policy Framework, specifies which servers are allowed to send email on behalf of your domain. When you send an email, the receiving server checks your SPF record in your DNS settings. If your sending server isn’t on that authorized list, the email fails SPF and likely goes to spam.
Setting up SPF means creating a DNS record that lists all the services that send email for you. This typically includes your email provider like Google Workspace, your cold email sending tool like Instantly or Lemlist, and any other service that sends email on your behalf. Your SPF record starts with “v=spf1” and includes statements for each authorized service.
The key is to use a hard fail policy rather than a soft fail. A hard fail tells receiving servers to reject emails that don’t come from authorized sources. You’ll also want to make sure you don’t exceed 10 DNS lookups in your SPF record, which means combining services where possible to stay under that limit.
DKIM: Your Digital Signature
DKIM, or DomainKeys Identified Mail, adds a digital signature to every email you send. It proves the email wasn’t tampered with in transit and that it really came from your domain.
Here’s how it works: your email server signs outgoing emails with a private key that only you have. Then you publish the corresponding public key in your DNS records. When someone receives your email, their server uses that public key to verify the signature matches. If it does, DKIM passes.
Most email providers and sending tools generate DKIM keys for you automatically. You just need to add the DNS record they provide to your domain settings. The record includes a selector (usually something like “default” or “s1”), followed by “_domainkey” and your domain name.
DMARC: Tying It All Together
DMARC, or Domain-based Message Authentication, Reporting and Conformance, ties SPF and DKIM together. It tells email providers what to do when authentication fails and gives you reports on who’s sending email using your domain.
Your DMARC record includes a policy that can be set to none, quarantine, or reject. When you’re first starting out, use the “none” policy, which monitors authentication but doesn’t affect delivery. This lets you see what’s happening without breaking anything.
After running with “none” for a couple weeks and confirming everything passes, move to “quarantine,” which sends authentication failures to spam. Eventually, you can move to “reject” for maximum protection, which blocks failed emails completely.
The best part about DMARC is the reporting. You’ll get regular reports showing all email sent from your domain, which helps you catch issues early and spot unauthorized senders trying to impersonate you.
Verifying Your Setup
Before you send a single cold email, verify your authentication is working. Tools like MXToolbox let you check your SPF, DKIM, and DMARC records directly. Mail Tester gives you a score after you send it a test email. GlockApps provides full inbox placement testing across different providers.
You should see all three protocols passing: SPF pass, DKIM pass, DMARC pass. If any fail, fix them before moving forward. Sending without proper authentication is like showing up to airport security without ID—you’re not getting through.
Pillar 2: Domain and IP Reputation
Authentication gets you in the door. Reputation determines whether you stay.
Email providers track your sending history obsessively. They watch how often recipients mark you as spam, your bounce rate, whether people engage with your emails through opens and replies, and if you’re sending to valid addresses. Good behavior builds good reputation, which gets you to the inbox. Bad behavior tanks your reputation and sends you straight to spam.
The Warmup Process
Here’s where most people mess up. They buy a new domain, set up authentication, and immediately blast out 1,000 cold emails. That’s a guaranteed ticket to spam.
New domains and email accounts have zero reputation. Email providers see this sudden volume from an unknown sender and flag it as suspicious. You need to build reputation gradually through a process called warming up.
The warmup process works like this: In your first week, send only 5 to 10 emails per day. Make sure these go to engaged recipients who will actually open and reply. Use warmup tools that simulate real engagement by connecting your inbox to a network of other users who automatically open, reply, and mark your emails as “not spam.”
By week two, you can increase to 20 to 30 emails per day while continuing your warmup activities. Start mixing in real prospects, but keep the volume low. Week three, bump up to 40 to 50 emails per day, monitoring deliverability closely. If you see any issues, scale back.
After week four, you can maintain 50 to 100 emails per mailbox per day. Keep your warmup tools running in the background indefinitely—they help maintain your reputation even after you’re established.
Best Warmup Tools for 2025
The top warmup tools we recommend are Instantly at $37 per month and up, which includes built-in warmup with your sending platform. Lemwarm runs $29 monthly for standalone warmup if you’re using a different sending tool. Warmbox is a budget option at $15 per month, while Mailwarm at $79 per month is best for high-volume operations.
These tools work by connecting your inbox to a network of other users. Emails are automatically sent and received between network members. Opens, replies, and “not spam” actions happen automatically, building your reputation with email providers without you lifting a finger.
The Secondary Domain Strategy
Never, ever send cold emails from your primary business domain. If something goes wrong—and eventually something will—you don’t want yourcompany.com blacklisted. That’s your main domain for customer communication, support tickets, and transactional emails. Keep it pristine.
Instead, buy 2 to 3 secondary domains that are variations of your main domain. If your company is at yourcompany.com, grab yourcompany.io, getyourcompany.com, or tryyourcompany.com for cold outreach. Rotate between them. If one gets burned, you have backups ready to go.
Monitoring Your Reputation
Check your domain reputation regularly using free tools. Google Postmaster Tools is essential for Gmail delivery and shows your reputation, spam rate, and authentication status. Microsoft SNDS helps you monitor delivery to Outlook. Talos Intelligence provides IP reputation lookups.
Watch for warning signs: reputation dropping from “High” to “Medium” or “Low,” increasing spam complaints, decreasing open rates, or bounce rates climbing. If you see any of these, stop sending immediately and diagnose the problem before continuing.
Pillar 3: Content That Avoids Spam Filters
Even with perfect authentication and a stellar reputation, bad content will trigger spam filters. Email providers use sophisticated algorithms to analyze your content for spam signals, and they’re getting better at it every year.
Avoiding Spam Trigger Words
Certain words and phrases are red flags to spam filters. Words like “free,” “guarantee,” “no obligation,” “act now,” “limited time,” “cash,” “money,” “earn,” “click here,” and “congratulations” all trigger spam filters when used in subject lines or body copy.
The trick is finding better alternatives. Instead of “Free consultation,” try “Quick question about [specific topic].” Replace “Limited time offer” with “Noticed something about [their company].” Don’t use “Click here”—just use the actual link text like “Check out the case study.”
Real personalization beats template language every time. Reference something specific about their company, a recent announcement, or a challenge in their industry. Spam filters look for generic templates. Personalized emails get through.
Links, Images, and Formatting
For cold emails, less is more. Stick to a maximum of 1 to 2 links per email. Never use link shorteners like bit.ly—they’re associated with spam. Avoid tracking pixels from unknown domains. Don’t link to brand new or suspicious domains.
Images are even more problematic. For cold outreach, use zero images. Plain text performs best because it looks like a real person writing to another real person. If you absolutely must use HTML, keep it minimal—basic formatting only.
The Perfect Cold Email Format
The highest-performing cold emails for deliverability follow a simple structure. Start with a personalized subject line that contains no spam words. Open with the recipient’s first name. Include 1 to 2 sentences of context or personalization showing you’ve researched them. Follow with 1 to 2 sentences explaining your value proposition. End with a clear, simple call to action—usually just a question. Sign off with your name, title, and company.
What to avoid: long signatures stuffed with images and links, multiple calls to action competing for attention, walls of text that look like spam, and generic templates that could be sent to anyone.
Plain Text Beats HTML
For cold email, plain text wins on deliverability every time. It looks personal, has no HTML flags that trigger spam filters, and mimics how real people actually email each other. Minimal HTML can work if you need some basic formatting, but it carries more risk. Rich HTML with images, buttons, and complex layouts triggers spam filters consistently.
| Format | Deliverability | Why |
|---|---|---|
| Plain text | Best | Looks personal, no HTML flags |
| Minimal HTML | Good | Some formatting, low risk |
| Rich HTML | Poor | Triggers spam filters |
Save the fancy HTML newsletters for marketing emails to your warm list. For cold outreach, keep it simple.
Your Pre-Launch Checklist
Before sending your first cold email campaign, work through this checklist to ensure everything’s properly configured. On the domain side, you need a secondary domain purchased and configured, at least two weeks old. Set up your SPF record, DKIM record, and DMARC record starting with the “none” policy. Configure a custom tracking domain if you’re using one.
For email accounts, create professional addresses using firstname@domain.com format. Add a profile photo to make the account look real. Configure a minimal email signature without images. Connect your warmup tool and let it run for at least two weeks before sending any real campaigns.
Your sending infrastructure should include your sending tool properly configured, daily limits set to a maximum of 50 emails per account, a sending schedule that operates during business hours in your prospects’ timezone, and reply handling set up so you don’t miss responses.
Finally, connect monitoring tools like Google Postmaster Tools, schedule weekly deliverability testing, and set up tracking for bounces and complaints.
Ongoing Maintenance and Monitoring
Deliverability isn’t set-and-forget. It requires ongoing monitoring and maintenance to keep your reputation healthy and your emails landing in the inbox.
Every week, check Google Postmaster Tools for reputation changes. Review your bounce rates—they should stay under 2%. Check spam complaint rates, which should remain under 0.1%. Run a deliverability test with GlockApps or Mail Tester to see actual inbox placement. Review and clean your prospect lists, removing any bounced or invalid addresses.
Monthly tasks include auditing your email content for spam triggers, reviewing sending patterns and adjusting volumes based on results, checking domain age and reputation scores, updating authentication records if anything changed, and rotating domains if any show reputation decline.
When to Hit the Brakes
Stop sending immediately if you see any of these red flags: bounce rate climbing above 5%, spam complaints exceeding 0.5%, open rates dropping suddenly without explanation, reputation plummeting from High to Low in Google Postmaster Tools, or blacklist warnings from any major provider.
These are signs of serious issues that will only get worse if you keep sending. Pause, diagnose the root cause, fix it, and then resume cautiously.
Troubleshooting Common Problems
When emails start going to spam, work through diagnostics systematically. First, check authentication using MXToolbox—make sure SPF, DKIM, and DMARC all pass. Second, check domain reputation in Google Postmaster Tools. Third, test your actual email content using Mail Tester. Fourth, review recent changes in your content, lists, or sending volume that might explain the issue.
Common fixes include correcting authentication gaps, reducing sending volume to rebuild reputation, removing spam trigger words from your copy, cleaning your list by removing bounces and unengaged contacts, and simply waiting while your reputation recovers.
If open rates drop suddenly, it could be a deliverability issue with emails going to spam, degraded list quality, subject lines triggering filters, or changed sending times affecting when people see your emails. Run a deliverability test first. If inbox placement is fine, the problem is your content or list quality, not technical deliverability.
Getting blacklisted requires immediate action. Stop all sending from the affected domain. Identify which blacklist flagged you using MXToolbox. Follow that blacklist’s specific delisting process. Investigate the root cause—was it a bad list, too much volume, or something else? Fix the underlying issue before you even think about resuming.
Prevention is easier than cure. Never buy email lists. Always verify email addresses before sending. Keep volume reasonable. Monitor reputation continuously. These simple practices prevent most blacklist issues.
Key Takeaways
Cold email deliverability is the foundation that everything else is built on. Without it, your carefully crafted messages, your personalized outreach, your compelling offers—none of it matters because nobody sees it.
Set up SPF, DKIM, and DMARC before sending a single cold email. These authentication protocols prove you’re legitimate and dramatically improve inbox placement. Warm up new domains for 2 to 3 weeks minimum before scaling to higher volumes. This builds the reputation you need with email providers.
Keep daily volume under 50 emails per mailbox to protect your reputation. Higher volume might seem tempting, but it’s not worth the risk to your domain. Test deliverability weekly with GlockApps or Mail Tester so you catch issues early before they tank your campaigns.
Monitor bounce rates and spam complaints religiously, keeping both under 2%. These metrics are early warning signs of deliverability problems. Address them immediately when they start climbing.
Get deliverability right, and everything else becomes easier. Your open rates improve. Your reply rates increase. Your campaigns actually generate results. Get it wrong, and nothing else matters—you’re just shouting into the void.
Need Help With Deliverability?
We’ve set up cold email infrastructure for over 50 companies, and our systems consistently achieve 95%+ inbox placement. We know what works because we’ve tested everything, made all the mistakes, and refined our approach over hundreds of campaigns.
If you’re struggling with deliverability or want to set things up right from the start, book a call with our team. We’ll audit your current setup, identify what’s holding you back, and show you exactly how to fix it. Let’s get your emails to the inbox where they belong.