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Why Are My Emails Bouncing Back?
Email bounces happen when a message cannot be delivered to the recipient. The bounce-back message (also called a Non-Delivery Report or NDR) contains important clues about what went wrong.
Common Bounce Reasons
- "550 No such user" or "User unknown": The email address you sent to does not exist. Double-check the spelling.
- "552 Mailbox full": The recipient mailbox is over its quota and cannot accept new messages.
- "554 Message rejected" or "blocked": The receiving server rejected your message, often due to spam filtering. Check your SPF and DKIM records in cPanel > Email Deliverability.
- "421 Too many connections": You are sending too many emails too quickly. Slow down the sending rate.
- "550 IP blacklisted": Your server IP may be on a spam blacklist. Contact support and we will investigate and request delisting.
What to Do
Read the bounce message carefully. It almost always tells you exactly why delivery failed. If the error references a blacklist, spam reputation, or authentication failure, make sure your SPF, DKIM, and DMARC records are properly configured (see our article on Email Authentication). If you cannot resolve the issue, forward the complete bounce message to our support team and we will help.
