Overview

Sender blocks occur when email providers reject an email before it reaches the recipient. These blocks often result from reputation issues, authentication failures, or recipient-side rules. Monitoring and resolving sender blocks is key to maintaining healthy deliverability.

Common Causes of Sender Blocks

Sender blocks occur due to a variety of factors, including:

1. Poor Sender Reputation
   1. High spam complaints
   2. Low engagement
   3. High bounce or unsubscribe rates
2. Missing or Invalid Authentication
   1. SPF, DKIM, or DMARC not set or misconfigured
   2. Mismatch between sending domain and “From” address
3. Blacklisted IP or Domain
   1. Your sending IP or domain appears on one or more public blacklists
4. Recipient-Side Filtering
   1. Email provider or company policy blocks specific senders or domains
   2. Overuse of keywords or formatting resembling spam

How to Prevent Sender Blocks

Sender blocks can be prevented by ensuring the following:

• Authenticate your domain: Ensure SPF, DKIM, and DMARC records are correctly set
• Monitor engagement: Remove unengaged contacts and suppress inactive users
• Maintain list hygiene: Regularly clean invalid or low-quality contacts
• Avoid spammy content: Limit use of aggressive language, all-caps, and heavy formatting

What to Do if You’re Blocked

If emails are sender blocked, here are some ways to help resolve the issue:

• Review the bounce or block error for clues
• Check your DNS and email headers for authentication issues
• Reach out to the recipient’s mail admin (if known) or support for delisting
• Contact Heymarket support if you need help investigating block events