SMTP Error 523:

What does it mean? And How to resolve this error.

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Error Description

SMTP error 523 is a permanent or "5xx" error code returned by a mail server to indicate that the recipient's mailbox or email account does not exist. This error signifies that the server cannot deliver the email because the specified recipient address is invalid or does not correspond to a valid user or mailbox.

What's Causing This Error

SMTP error 523 is primarily caused by the following reasons:

  • Non-existent email address: The recipient's email address provided in the "RCPT TO" command or the "To:" field of the email message is incorrect or does not correspond to an active email account on the recipient's domain.
  • Misspelled or incomplete email address: The email address may contain typographical errors, missing characters, or incorrect domain names, making it impossible for the server to route the email correctly.
  • Deleted or inactive mailbox: The recipient's email account may have been deleted, suspended, or marked as inactive, rendering it unavailable for receiving emails.

How to fix SMTP Error 523 Error?

  • Double-check recipient address: Ensure that the recipient's email address is spelled correctly, is complete, and includes the correct domain name. Common mistakes, such as missing "@" symbols or typographical errors, should be corrected.
  • Verify recipient's mailbox status: Confirm with the recipient that their email account is active and operational. If the mailbox has been suspended or deleted, they will need to take steps to reactivate it or provide an alternative email address.
  • Investigate domain configuration: If the recipient's domain is misconfigured or has DNS (Domain Name System) issues, it may result in SMTP error 523. In such cases, the recipient's email administrator may need to resolve the domain-related problems.

Example 1: "523 5.1.1 Recipient address does not exist."

Example 2: "523 5.1.2 Invalid email address format."

Example 3: "523 5.5.1 Recipient mailbox is currently suspended."

Example 4: "523 5.7.1 Domain configuration error. Email delivery cannot be completed."