Why Are My Transactional Emails Going to Spam?

Cause 1: Authentication Problems

The most common cause of transactional email spam filtering is failed authentication.

Common Authentication Failures

• Missing SPF: Sending server not authorized in SPF record
• Broken DKIM: Signature invalid or key not published
• DMARC failure: Neither SPF nor DKIM passes with alignment
• New sending source: Recently added service not yet in SPF

How to Diagnose

1. Send a test email to a personal account
2. View full message headers
3. Look for Authentication-Results header
4. Check for spf=pass, dkim=pass, dmarc=pass

How to Fix

• Add missing sending sources to SPF record
• Verify DKIM selector and key are correct in DNS
• Ensure From domain aligns with SPF or DKIM domain
• Test authentication after each change

Cause 2: Reputation Contamination

If transactional and marketing email share the same domain, marketing problems affect transactional delivery.

How This Happens

• Marketing campaign generates high complaints
• Domain reputation drops
• All email from that domain—including transactional—gets filtered

Signs of Reputation Contamination

• Transactional spam problems coincide with marketing campaigns
• Google Postmaster Tools shows domain reputation decline
• Problem affects all email types, not just one

How to Fix

• Separate transactional onto its own subdomain
• Build clean reputation on the transactional subdomain
• Fix marketing practices to prevent future contamination

Cause 3: Content Triggers

Even properly authenticated email can trigger content-based spam filtering.

Common Content Issues

• Suspicious links: Shortened URLs, mismatched display/actual URLs
• Too much promotional content: Upsells in order confirmations
• Image-heavy templates: Low text-to-image ratio
• Spam-associated words: Even in legitimate context

How to Fix

• Use full, transparent URLs (no shorteners)
• Keep transactional emails focused on the transaction
• Include adequate plain text content
• Avoid unnecessary promotional elements

Cause 4: Sending Infrastructure Issues

IP Reputation

• New IP without warmup
• Shared IP with poor senders
• IP on blocklist

Inconsistent Sending

• Sudden volume spikes trigger defensive filtering
• Long gaps between sends lose established patterns

Diagnosing the Specific Cause

Check Headers First

Email headers reveal authentication status and filtering reasons:

• Authentication-Results shows SPF, DKIM, DMARC status
• X-Spam-Status may show scoring factors
• X-Microsoft-Antispam shows Microsoft-specific data

Compare Working vs Non-Working

If some transactional emails work and others don't:

• Compare headers between successful and failed emails
• Identify what differs (content, links, sender)
• Test changes individually to isolate the cause

Quick Fixes for Urgent Issues

1. Verify authentication: Most common cause, check first
2. Check blocklists: Use MXToolbox to scan your IP
3. Review recent changes: New email template? New sending service?
4. Check reputation tools: Google Postmaster, Microsoft SNDS