Emails Going to Spam? 10 Rules to Improve Your Email Deliverability [Tips]

You have a great offer and a well-written email, but still no replies? Maybe your message didn’t even reach the recipient. Before you assume cold emailing doesn’t work, check if your email was blocked by a spam filter.

In this article, you’ll find answers to these questions:

• Why do your emails end up in spam even when everything seems fine?
• What do spam filters check before deciding whether to deliver your email?
• How can you increase the chances that your cold email gets delivered and opened?

Before you send your first email: Warm up your domain and inbox

No, this is not a joke. Sending emails from a freshly created domain is like jumping into deep water without learning how to swim.

What does it mean to "warm up" a domain?

• Start by sending emails to contacts who will definitely open and reply (even with a test reply),
• Spread your email sending over weeks, not a single day (e.g., 20 emails/day during the first week),
• Avoid mass emailing to cold contacts during the first 2–3 weeks,
• Connect your domain to a professional inbox (e.g., Google Workspace or Outlook),
• Set up SPF, DKIM, and DMARC – the three magic acronyms that make your emails "trusted."
  
  

TIP: Use tools like MailTester, Warmup Inbox, Instantly Inbox Placement or MXToolbox to test the quality and deliverability of your inbox and automate the domain and inbox warm-up process.

How to warm up your inbox?

The inbox warm-up process is usually automated using specialized tools like Warmup Inbox or cold mailing platforms with warm-up modules, such as Woodpecker, Instantly or Lemlist.

Here’s how it works:

• Connect your properly configured inbox to the selected tool (they all offer clear onboarding instructions),
• Warm up gradually over a minimum of 2–3 weeks.

Two example methods for warming up:

Method I – Only warm-up – 3–4 weeks

• Start by sending 5 emails per day,
• Add 5 more emails to the sequence daily (e.g., 10 emails on Day 2, 15 emails on Day 3, and so on),
• Reach 50 emails per day by Day 10,
• Maintain this sending volume for another 5–10 days before launching your campaign.

Method II – Warm-up + early campaign launch – 2–3 weeks

• Start by sending 10 emails per day,
• Add 7 more emails daily (e.g., 17 on Day 2, 24 on Day 3, etc.),
• Reach 50 emails per day by Day 6,
• Maintain this level for 5 days,
• Then reduce warm-up sending volume by half (to max 25 warm-up emails/day) and simultaneously start sending up to 25 cold emails per day to prospects.

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What influences cold email deliverability?

• Proper DNS configuration: SPF, DKIM, DMARC (explained below),
• Domain and IP reputation: Never send from your main business domain. Create a subdomain, e.g.:
  
  • Main domain: yourcompany.com
  • Cold mailing domain: yourcompany.net
    
• Email content: Natural, specific, and avoids "spammy" words flagged by Google like free, promotion, urgent, guaranteed profit, etc.
  (Tip: Woodpecker offers a spam word checker module.)
• Variation: Avoid sending hundreds of identical emails. Change first names, company names, CTAs, subjects, greetings.
• Personalization: Mention the recipient’s company, offer, or real activities.
• Email length: 50–125 words is the golden standard. The shorter, the better – without losing the message.
• Fonts and formatting: Black text, white background, one font, no underlining, no colorful buttons.
• Signature with details: First name, last name, company, website link – everything that builds trust.

TIP: Always test your emails in anti-spam tools like MailTester (for domain reputation) or Warmup Inbox (to check inbox placement).

Configure your DNS: SPF, DKIM, DMARC

What do they do?
They tell email servers: "Hey, this email is legit."

• SPF record: Authorizes a specific IP server to send emails on behalf of your domain. Without it, spammers could impersonate your domain.
• DKIM record: Adds an encrypted "key" to outgoing emails. If the recipient server can validate it, it trusts that the email comes from the domain owner.
• DMARC record: Sets rules for what happens if an email fails SPF/DKIM checks (block, quarantine, or deliver). It also sends reports about suspicious activities involving your domain.

TIP: You can check your DNS records for free using MXToolbox.

Limit your bounce rate

Spam filters hate when you send emails to invalid addresses.
It's better to send 50 verified emails than 5000 random ones.

How to reduce bounce rate?

• Never buy ready-made contact databases,
• Regularly clean inactive email addresses,
• Verify your email lists with tools like Bouncer, NeverBounce, ZeroBounce, etc.
  
  

We’ve also created a separate guide on How to Find a Potential Client's Email? 8 Effective Methods and a Comparison of the Best Email Search Tools in 2025 – check them out if you need help preparing a quality contact database.

Have questions? Want to discuss your campaign?

Get in touch — I’ll help you set up your cold email campaign so your emails get delivered and convert.