You can write the best cold email in the world, target the perfect prospect, and craft a subject line that demands attention. But if that email lands in the spam folder, none of it matters. Deliverability is the foundation that every cold email campaign is built on, and most companies get it wrong.
This guide covers everything you need to know about cold email deliverability in 2026 -- from technical setup to content best practices to ongoing monitoring.
Why Deliverability Has Gotten Harder
Email service providers like Google and Microsoft have significantly tightened their spam filters over the past two years. Google's 2024 sender requirements, which were expanded in 2025, now require strict authentication, low spam complaint rates (under 0.1%), and easy one-click unsubscribe mechanisms. Microsoft followed with similar requirements for Outlook.
For cold email senders, this means the days of bulk-sending from a single domain with minimal setup are over. You need a professional infrastructure, disciplined sending practices, and content that earns its place in the inbox.
Technical Setup: The Non-Negotiable Foundation
Before you send a single cold email, these technical elements must be in place:
Separate sending domains. Never send cold email from your primary business domain. If your deliverability takes a hit, you do not want it affecting your regular business communications. Purchase secondary domains that are similar to your primary domain. For example, if your company is acme.com, use domains like acme-mail.com, getacme.com, or tryacme.com.
SPF (Sender Policy Framework). This DNS record tells receiving servers which IP addresses are authorized to send email on behalf of your domain. Without it, your emails look suspicious and are more likely to be filtered.
DKIM (DomainKeys Identified Mail). This adds a cryptographic signature to your emails that verifies they have not been tampered with in transit. It is a trust signal that receiving servers rely on heavily.
DMARC (Domain-based Message Authentication, Reporting & Conformance). This policy tells receiving servers what to do with emails that fail SPF or DKIM checks. Start with a monitoring policy (p=none) and move to a quarantine or reject policy once you have confirmed everything is working correctly.
Custom tracking domain. If you use an email sending tool that tracks opens and clicks, set up a custom tracking domain instead of using the tool's default shared tracking domain. Shared domains accumulate reputation from all users -- including spammers.
Domain Warm-Up: Patience Pays Off
New domains have no reputation with email service providers. Sending cold emails from a brand-new domain is like applying for a mortgage with no credit history -- you will be treated with maximum suspicion.
Domain warm-up is the process of gradually building a positive sending reputation over 2 to 4 weeks. Here is a typical warm-up schedule:
- Week 1: Send 5 to 10 emails per day, primarily to contacts who will reply (warm contacts, team members, friends who know to respond)
- Week 2: Increase to 15 to 25 emails per day, mix of warm contacts and initial cold prospects
- Week 3: Increase to 30 to 50 emails per day, primarily cold prospects
- Week 4: Scale to your target sending volume, typically 50 to 100 emails per day per inbox
During warm-up, prioritize getting replies and engagement. Open the emails sent to you, reply to them, mark them as important, and move them out of spam if they end up there. This engagement signals to ESPs that your domain sends mail people want to receive.
Many teams use automated warm-up tools that simulate this engagement at scale. These tools work, but they should supplement real engagement, not replace it entirely.
Content Rules for Inbox Placement
Once your technical setup is solid and your domains are warmed, the content of your emails becomes the primary factor in deliverability. Here are the rules:
Avoid spam trigger words. Words like "free," "guarantee," "act now," "limited time," "click here," and "buy now" are red flags for spam filters. This does not mean you can never use them, but be aware that their presence increases your spam score.
Minimize links. Include no more than one link per cold email, and ideally use a link only in your email signature or a specific CTA. Multiple links look like marketing emails, not personal outreach.
No images in the first email. Images increase email file size and look like marketing content. Save images for later in the sequence when the prospect has already engaged.
Keep emails short. Longer emails have lower deliverability rates. Aim for 50 to 150 words. If you need to say more, schedule a call.
Write like a human. Emails that look like they were written by a real person to a specific individual perform better than polished marketing copy. Use casual language, short paragraphs, and a conversational tone. Run your drafts through our cold email grader to check before sending.
Personalization helps deliverability. When every email is slightly different because of personalized elements, spam filters are less likely to flag your messages as bulk email.
Sending Practices
How you send matters as much as what you send:
- Limit volume: Do not exceed 50 to 100 emails per inbox per day. If you need to send more, add more inboxes and domains.
- Spread sending throughout the day: Do not blast 100 emails in 5 minutes. Spread them over 4 to 6 hours to mimic human sending patterns.
- Use multiple inboxes per domain: 2 to 3 email addresses per domain, each sending 30 to 50 emails per day.
- Rotate domains: Have 3 to 5 sending domains in rotation so no single domain bears the full sending burden.
- Respect time zones: Send during the recipient's business hours for higher engagement.
Monitoring and Maintenance
Deliverability is not a set-it-and-forget-it task. You need ongoing monitoring:
- Check bounce rates daily. If bounce rates exceed 5%, stop sending and clean your list. High bounce rates destroy sender reputation fast.
- Monitor spam complaint rates. Keep them under 0.1%. If you are getting complaints, your targeting or messaging needs work. Consider partnering with a dedicated appointment setting service that manages deliverability for you.
- Track inbox placement rates. Use tools that test whether your emails are landing in the inbox, spam, or promotions tab across major providers.
- Watch for blacklists. Regularly check whether your sending IPs or domains appear on email blacklists. If they do, take immediate action to delist.
Deliverability is not glamorous. No one gets excited about SPF records and warm-up schedules. But it is the difference between a campaign that generates 25 meetings and one that generates zero. Get this right first, and everything else becomes easier.
The companies that consistently win at cold email are not the ones with the cleverest copy. They are the ones with the most disciplined infrastructure and sending practices. Treat deliverability as the foundation it is, and your cold email campaigns will outperform the competition.