What does 553 mean?

• SMTP 553 indicates mailbox name issues:
• What it means:
• The mailbox name in the address is not valid. The format may be wrong or violate server policies.
• Common causes:

Invalid address format: Malformed email address. Policy violation: Address type not allowed. Character restrictions: Unsupported characters in address. Role address rejection: Server blocking certain address types.

• Typical message examples:
• "553 Mailbox name not allowed" "553 Invalid recipient" "553 Requested action not taken: mailbox name not allowed"
• Response:
• Verify the address format is correct. Check for typos or encoding issues. Suppress if address is confirmed invalid.
• 553 says "that name is not valid here." Check the address format and spelling.