I'm not sure if you refer to the "Authorized TO" whitelist, or to the new feature present in SpamFilter v4.2.

If the question is for the "Authorized TO", this section of our manual for the following parameter in the SpamFilter.ini file should provide the answer:

If you're referring to the new feature in SpamFilter v4.2 that checks to ensure your destination SMTP server accepts the recipients, placing "on hold" the remote server while this check is being made, then the behavior should be straightforward. If one or more of the recipients is not accepted by your mail server, SpamFilter will deliver the email to the valid recipients, but will also output a 500 error code to the remote server to inform it the email was not delivered successfully. The 500 error code will include in its description a list of the email addresses that were not delivered.