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.