If an outbound message fails to reach its destination, the receiving mail server returns a non-delivery report (NDR) containing an error code. Below is a translation guide for the most common delivery failures.
Common Error Translation Directory
1. 550 User Unknown / No Such User Here
- What it means: The target mailbox username you specified does not exist on the destination network server.
- How to resolve: Verify the recipient's address spelling or check for typos (e.g.,
.coninstead of.com).
2. 552 Message Rejected / Mailbox Quota Exceeded
- What it means: Your recipient's storage box is full, preventing them from receiving new messages.
- How to resolve: Contact the recipient through an alternative channel to let them know their inbox is full, or compress your file attachments to reduce message size.
3. 554 or 550 Blocked / Sender IP Blacklisted
- What it means: The security filters on the recipient's server have blocked your website hosting server's IP address, often because another account on your shared hosting environment sent spam.
- How to resolve: Contact our support team immediately and include the complete bounce error text. We will inspect the IP address and request its removal from blacklists.
4. SPF/DKIM Authentication Failures
- What it means: The receiving network rejected your mail because it failed validation checks against your domain's SPF or DKIM security records.
- How to resolve: Review our Knowledge Base guide on setting up SPF, DKIM, and DMARC in cPanel to update your DNS authentication entries.
