Email deliverability: the complete guide for 2026

Email deliverability refers to your ability to land emails in your recipients' primary inbox rather than spam, promotions, or having them blocked entirely. It's determined by a complex interplay of factors:

SPF is a DNS record that specifies which IP addresses and servers are allowed to send email on behalf of your domain. When a receiving server gets an email claiming to be from your domain, it checks your SPF record to verify the sender is authorized.

How to set up SPF:

1. Identify all services that send email from your domain (your email provider, marketing tools, CRM, etc.)
2. Create a TXT record in your DNS with the SPF information
3. Include all authorized senders in one SPF record (you can only have one)

SPF best practices:

• Keep a single SPF record (only one is processed)
• Stay within the 10 DNS lookup limit
• Include all sending services
• End the record with "~all" or "-all" rather than "+all"

DKIM adds a digital signature to your emails that proves they haven't been modified in transit and genuinely originated from your domain. It works through public/private key cryptography.

How DKIM works:

1. Your email server signs outgoing emails with a private key
2. The public key is published in your DNS records
3. Receiving servers use the public key to verify the signature

Setting up DKIM:

• Most email providers generate DKIM keys for you
• You'll add a TXT record to your DNS with the public key
• Each sending service needs its own DKIM record (unlike SPF)

DMARC ties SPF and DKIM together and tells receiving servers what to do when authentication fails. It also provides reporting so you can monitor who's sending email from your domain.

DMARC policies:

• p=none: Monitor only, failing emails are delivered as usual
• p=quarantine: Send failing emails to spam
• p=reject: Block failing emails entirely

Best practice: Start with p=none to monitor, then gradually move to quarantine and eventually reject as you confirm legitimate sending is working.

If you're sending from a new domain or IP address, you need to "warm it up" before sending at volume. Make sure your domain setup is complete first. Email providers are cautious with new senders and throttle or block emails until a domain has an established sending history.

Why domain warming matters

When Gmail, Microsoft, or other providers see a new domain suddenly sending thousands of emails, their spam filters go on high alert. The domain has yet to build a reputation, so it could be a spammer.

Domain warming builds your sender reputation gradually by:

• Starting with small sending volumes
• Slowly increasing over 2-4 weeks
• Establishing positive engagement signals
• Building trust with email providers

• Start with your best contacts: People who have previously engaged with your emails
• Send consistently: Daily sending is better than sporadic bursts
• Monitor your metrics: Watch bounce rates, spam complaints, and open rates
• Use human-like patterns: Send during business hours, like a real person would
• Keep content free of spam triggers: Use plain, conversational wording during the warming period

Your sender reputation is like a credit score for email. It's constantly calculated based on your sending behavior and determines how email providers treat your messages. Good sender management is essential to keeping it healthy.

Factors that affect sender reputation

How to maintain good reputation

Your content matters as much as authentication and reputation. Here's how to keep it filter-friendly:

Spam trigger words

While modern spam filters are more sophisticated than simple keyword matching, certain words and phrases still increase spam risk:

• Financial: "Free," "Money back," "No obligation," "Winner"
• Urgency: "Act now," "Limited time," "Urgent," "Immediately"
• Promises: "Guaranteed," "Risk-free," "100%," "Promise"
• Formatting: ALL CAPS, excessive punctuation!!!, lots of $$$

Content best practices

• Balance text and images: Always pair images with real text
• Use a reasonable text-to-HTML ratio: Include enough text content
• Limit links: One or two relevant links look the most legitimate
• Use full, branded URLs: Shorteners are commonly used by spammers
• Include physical address: Required by CAN-SPAM and looks legitimate
• Use a real reply-to address: Pick a monitored inbox over no-reply@

Dedicated vs. shared IPs

For most B2B senders doing under 100,000 emails per month, shared IPs from a reputable email provider are fine.

Multiple sending domains

Many companies use separate domains for different email types:

• Transactional: notifications@company.com
• Marketing: marketing.company.com or company-mail.com
• Outbound sales: outreach.company.com

This protects your primary domain reputation if one type of email runs into issues. Pairing multiple domains with inbox rotation further improves deliverability at scale.

Email deliverability is becoming more sophisticated. Here's what to watch:

Deliverability is an ongoing practice. Build your foundation with proper authentication, maintain your reputation through good sending practices, create content that provides value, and monitor your metrics continuously.

The best email marketers treat deliverability as a core competency from day one. When you get it right, you go beyond the inbox: your carefully crafted messages actually reach and resonate with your audience.