SMTP 553 typically indicates an invalid recipient address format or prohibited mailbox name. Learn what to check.
SMTP 553 is a permanent rejection that usually points to an invalid email address format or a mailbox name that the server refuses to accept.
Confirm syntax, remove illegal characters, and validate that your list data isn’t corrupted. These should be treated as hard bounces and suppressed.
Related Keywords
smtp 553553 error emailinvalid mailbox nameaddress syntaxhard bounce