Error Description

SMTP error 556 is a permanent or "5xx" error code returned by a mail server to indicate that it has rejected an email message due to issues with the sender's email address or domain. This error signifies that the email message cannot be delivered because of problems with the sender's information.

What's Causing This Error?

SMTP error 556 can be caused by several reasons, including:

• Non-existent sender: The sender's email address provided in the "MAIL FROM" command or the "From:" field of the email message does not correspond to a valid email account or mailbox.
• ‍Invalid sender domain: The sender's email domain (e.g., example.com) does not exist, has expired, or has DNS (Domain Name System) issues.
• ‍Unauthorized sender: The sender's domain or email address is not authorized to send email to the recipient or is blocked by the recipient's server for policy reasons.
• ‍Content filtering: The email message's content may contain prohibited content, such as spam, malware, or other violations of the recipient server's policies.

How to fix SMTP Error 556?

• Verify sender's email address: Ensure that the sender's email address is spelled correctly, is complete, and corresponds to a valid email account or mailbox.
• Check sender domain: Confirm that the sender's email domain is functioning correctly, does not have DNS issues, and is not experiencing policy-related blocking.
• ‍Contact sender administrators: If the sender's domain is experiencing issues, it may require intervention by the administrators to resolve technical problems or adjust email sending policies.
• ‍Review email content: Check the content of the email message for potential policy violations, such as spammy content or malicious attachments, and ensure it complies with the recipient server's policies.

SMTP Error 556 Examples

Example 1: "556 5.1.1 sender@example.com: Sender address does not exist."

Example 2: "556 5.4.5 sender@example.com: Domain name not found. Check sender domain."

Example 3: "556 5.7.0 sender@example.com: Unauthorized sender. Email blocked due to policy reasons."

‍Example 4: "556 5.1.2 Content filtering detected prohibited content in the email message. Delivery denied."