The SMTP error code is from your email service provider. Either your email provider's server or your recipient's email server rejected the message due to content that appeared to be spam. Norton is merely displaying the bounceback notification, and had no involvement in the failure of the message to be delivered. I would suggest that you check with your email service provider if you need further clarification about the specific reason for the message rejection.
52 5.2.0 u2k81t0253BLhLf012k9TP Suspected spam message rejected. IB703- This error is sometimes generated by emails sent to the Bigpond (Australia) servers “@bigpond.com” when two or more recipients are included in the TO header. To resolve this, simply include one recipient email address in the TO header, and CC or BCC and other recipients.
A 552 email error is typically encountered when there is a problem related to an attachment in your email. Either it has exceeded the size limits of the remote server, or the file-type isn't allowed by the remote server. Some mail servers also seem to use this error code incorrectly when blocking a message due to triggering a filter such as a URL in the message being found in a domain black list. To properly address your concern, we'd like to know more information. Kindly answer the questions below: