SMTP
553 Mailbox Name Invalid
The requested action was not taken because the mailbox name is syntactically incorrect. The email address does not conform to the expected format.
When You See This Code
When the sender or recipient address contains invalid characters, improper formatting, or violates the server's naming conventions.
How to Fix
Check the email address format — ensure it follows the standard [email protected] pattern with valid characters. Remove any spaces, special characters, or encoding issues from the address.