Emails Going to Spam? Here's How to Fix It

Why emails go to spam (the 5 main causes)

Spam filters evaluate multiple signals. If enough signals are negative, your email lands in spam. The five most common causes for developer-sent email:

1. Missing or broken email authentication (SPF, DKIM, DMARC)
2. Poor sender reputation (domain or IP)
3. Content that triggers spam filters
4. Sending patterns that look suspicious (volume spikes, new domain)
5. Recipient engagement signals (people marking your email as spam)

Let's fix each one.

Step 1: Check your email authentication

This is the single most impactful fix. Without proper authentication, ISPs have no way to verify you're authorized to send from your domain.

SPF (Sender Policy Framework)

SPF tells receiving servers which IP addresses are allowed to send email for your domain. Add a TXT record to your DNS:

v=spf1 include:amazonses.com ~all

If you use RelayPost, the exact SPF record is provided in your domain verification dashboard.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to every email, proving it wasn't tampered with in transit. This requires adding a CNAME or TXT record to your DNS. RelayPost generates the DKIM key pair and provides the DNS record automatically.

DMARC (Domain-based Message Authentication)

DMARC tells ISPs what to do when SPF or DKIM fails. Start with a monitoring policy:

v=DMARC1; p=none; rua=mailto:[email protected]

Once you confirm everything passes, move to p=quarantine and eventually p=reject.

For detailed setup instructions, see our SPF, DKIM & DMARC guide.

Step 2: Check your domain reputation

Even with perfect authentication, a bad domain reputation will land you in spam.

• Use Google Postmaster Tools to check your domain reputation with Gmail
• Check Talos Intelligence for your IP reputation
• Search blocklists at MXToolbox

If your domain reputation is low, the fix is time + clean sending. Remove invalid addresses, honor unsubscribes immediately, and send only to engaged recipients.

Step 3: Review your email content

Content-based spam triggers to avoid:

• ALL CAPS in subject lines or body text
• Excessive exclamation marks or special characters
• Spam trigger phrases: "act now", "limited time", "free money", "click here"
• Image-only emails with no text content
• Shortened URLs (bit.ly, etc.) — use full URLs
• Missing unsubscribe link (required by CAN-SPAM and GDPR)
• Mismatched From name and domain

For transactional email, keep it simple: plain text or minimal HTML, clear subject line, relevant content.

Step 4: Check your sending patterns

ISPs watch for suspicious sending behavior:

• Sudden volume spikes — if you normally send 100 emails/day and suddenly send 10,000, that's a red flag
• New domain without warmup — new domains have no reputation. Start with small volumes and increase gradually over 4-8 weeks
• Inconsistent sending — sending nothing for weeks then blasting a large batch looks suspicious
• High bounce rates — if more than 2% of your emails bounce, ISPs assume you're sending to bad lists

Step 5: Monitor and maintain deliverability

Deliverability isn't a one-time fix. Monitor these metrics continuously:

• Bounce rate — keep below 2%. Remove invalid addresses immediately.
• Complaint rate — keep below 0.1%. If people mark your email as spam, stop sending to them.
• Inbox placement rate — use seed testing or RelayPost's public deliverability dashboard to track.

Frequently asked questions