Hi,
Based on the log you provided the email is not black listed only greylisted. Greylisting is a way to reduce spam. For more information on how it works please see this article:https://portal.smartertools.com/kb/a2692/enable-greylisting.aspx. A properly configure remote server should try to resend after the specified time (300 seconds) and as long as it does the message will be received and delivered to the users. If your users are not receiving an email from a specific server that server may not be configured to resend.