Troubleshooting Email Delivery: Fixing Bounces, Rate Limits, and Spam Filtering

Understanding Email Bounces#

When an outgoing email fails to reach its recipient, the mail server returns a Non-Delivery Report (NDR) with an SMTP status code:

• 550 5.1.1 User Unknown: The recipient email address does not exist. Check for typos in the domain or mailbox.
• 550 5.7.1 Message Rejected / Spam Blocked: The receiving server rejected your message due to missing SPF/DKIM or spam keywords.
• 421 4.7.0 Rate Limit Exceeded: The remote provider (e.g. Outlook/Hotmail) is temporarily throttling incoming connections.

How to Check cPanel Track Delivery#

cPanel includes an instant tracking tool showing the exact server handshake:

1. 1
   In cPanel, click Track Delivery under Email.
2. 2
   Enter the recipient email and click Run Report.
3. 3
   View the Delivery Status icon and click the info icon to read the full SMTP handshake response.