This error message indicates that the email you attempted to send was flagged as unsolicited mail (spam) by the recipient mail server. Most commonly, this issue arises when email providers like Gmail, Yahoo, or Microsoft detect that your message does not meet their spam and authentication policies.

Causes of the Error

Lack of Proper Email Authentication

Missing or misconfigured SPF, DKIM, and DMARC records.

Poor IP Reputation

Your server IP address might be blacklisted or have a poor sending reputation.

Spam-Like Content

The email contains spammy subject lines, excessive links, or keywords flagged as spam.

High Email Volume

Sending a large number of emails within a short period can trigger this error.

Unverified or Misconfigured Sending Domain

The domain used for sending the email is not properly verified or lacks DNS configuration.

Open Relays

Your email server may be configured as an open relay, allowing unauthorized sending.

Steps to Fix the Issue

Check and Configure SPF, DKIM, and DMARC

1

SPF (Sender Policy Framework)

Ensures that emails sent from your domain are authorized.

v=spf1 include:_spf.google.com ~all

Add this as a TXT record in your domain DNS settings.

2

DKIM (DomainKeys Identified Mail)

Digitally signs your email to prove authenticity.

  • Generate a DKIM key using your mail server.
  • Add the public key as a TXT record in your DNS.
3

DMARC (Domain-based Message Authentication, Reporting & Conformance)

Helps enforce SPF and DKIM policies.

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com

Check IP Reputation

Avoid Spammy Content

  • Use professional language and avoid words/phrases that trigger spam filters, such as:
    • "Congratulations!"
    • "Free money!"
    • Excessive exclamation marks or ALL CAPS.

Limit Sending Volume

  • Gradually increase email sending volume to avoid appearing as a spammer.
  • Stick to the recipient provider rate limits (e.g., Gmail typically allows 500 messages/day for personal accounts).

Verify Reverse DNS (PTR Record)

  • Ensure that your server IP address has a reverse DNS (PTR record) pointing back to your domain.

Use a Reputable Email Service Provider

If you are running your own mail server and encountering repeated issues:

Testing Your Fixes

  1. Send a Test Email:
    • Send a test email to a tool like Mail-Tester to analyze your SPF, DKIM, DMARC, and spam score.
  2. Check Email Headers:
    • Review email headers in the recipient inbox to verify SPF, DKIM, and DMARC authentication status.
  3. Monitor Email Delivery:
    • Use tools like Google Postmaster Tools or your email server logs to check delivery status and analyze rejection rates.

Example DNS Records for Email Authentication

Here is an example of DNS records for a properly configured mail domain:

Type Name Value
TXT @ v=spf1 ip4:192.168.1.1 include:_spf.google.com ~all
TXT default._domainkey v=DKIM1; k=rsa; p=YOUR_DKIM_PUBLIC_KEY
TXT _dmarc v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com
  1. Authenticate your emails with proper SPF, DKIM, and DMARC settings.
  2. Check your IP reputation and ensure it is not blacklisted.
  3. Avoid spammy email content and follow sending limits.