Avoid the Spam Folder: Best Practices for Email Deliverability

Last Updated on February 28, 2025 by Damien Hurwitz

Over 45% of all emails sent worldwide are spam. That’s nearly half of all emails! With inboxes flooded daily, email providers have become stricter about what lands in the inbox versus what gets buried in the spam folder. If your marketing emails aren’t reaching your audience, you’re losing out on engagement, conversions, and ultimately, revenue.

So, how can you improve email deliverability and ensure your messages reach the inbox? Let’s break it down.

1. Authenticate Your Emails

Think of email authentication as a passport for your messages. Without it, your emails are more likely to be flagged as suspicious. Set up these key authentication protocols:

• SPF (Sender Policy Framework): Specifies which mail servers are allowed to send emails on your behalf.
• DKIM (DomainKeys Identified Mail): Adds a digital signature to your messages, verifying their authenticity.
• DMARC (Domain-based Message Authentication, Reporting & Conformance): Ensures emails align with SPF and DKIM policies.

Without these, your emails may be viewed as spoofed or fraudulent, significantly lowering your chances of inbox placement.

2. Avoid Spam Trigger Words

Email filters scan for words that sound too pushy or gimmicky. Avoid phrases like:

• “Free money”
• “Act now!”
• “Congratulations, you won!”
• “100% guaranteed”

Instead, use natural, conversational language that adds value to your audience.

One trick is to read your email out loud before sending it. If it sounds overly promotional, it may be a red flag to spam filters.

3. Clean Your Email List Regularly

Sending emails to outdated or fake addresses hurts your sender reputation. Use email verification tools to remove inactive or invalid addresses. Also, encourage engaged subscribers to whitelist your email address to boost deliverability.

Some best practices include:

• Removing hard bounces immediately.
• Re-engaging inactive subscribers before removing them.
• Providing an easy opt-out option to prevent spam complaints.

4. Personalize Your Emails

Emails that feel impersonal are more likely to be ignored—or worse, marked as spam. Use the recipient’s name, tailor content to their interests, and segment your list based on behavior or demographics.

Segmenting your audience can significantly boost engagement. For example, send different content to new subscribers versus long-time customers.

5. Optimize Your Email Content

Avoid sending image-heavy emails with little text, as spam filters may flag them. Follow these best practices:

• Use a clear, engaging subject line (avoid ALL CAPS).
• Keep a healthy text-to-image ratio.
• Include an easy-to-find unsubscribe link.
• Try to avoid using ! or unusual characters in subject lines.

Subject lines are critical! Studies suggest that personalized and curiosity-driven subject lines have higher open rates.

Additionally keep in mind how different inboxes evaluate your incoming emails:

• Gmail: Engagement-based filtering, prioritizes responses and user actions.
• Yahoo: Heavy reliance on sender reputation, reacts harshly to spam complaints.
• Outlook (Microsoft): Strict on spam complaints, prefers authenticated senders (SPF, DKIM, DMARC enforced).
• Apple Mail: Affects tracking due to Mail Privacy Protection (MPP), making open rates unreliable.
• Other ISPs: Generally follow Gmail/Yahoo principles but may have unique blacklists and rate limits.

7. List Cleaning Practices for a Healthy Reputation

Regular list cleaning ensures a strong sender reputation and high deliverability. Follow these best practices:

• Remove Inactive Subscribers: Users who haven’t engaged in 3-6 months should be re-engaged or removed.
• Suppress Hard Bounces & Spam Complaints: Immediately remove these addresses from future campaigns.
• Use Double Opt-In: Ensures subscribers are genuinely interested.
• Monitor Engagement & Sunset Strategy: Gradually reduce sends to disengaged users before removing them.

Additionally some good monitoring services to use in tandem with your ESP are:

• Inbox Placement Testing: Tools like GlockApps, MailTester, or Seedlist testing services.
• Domain & IP Reputation: Google Postmaster Tools, Microsoft SNDS, Talos Intelligence.
• Bounce & Complaint Rates: ESP reports and third-party monitoring.
• Engagement Trends: Click-through rates (CTR), reply rates, and inbox placements matter more than open rates.
• Blacklist Monitoring: Check if your sending domain/IP is blacklisted using services like MXToolbox.