This will result in mail, that would previously have been bounced as 'spam content found', now finding it's way to the recipient's spam folder. Of course some individuals may choose to alter those settings, but in general all mail, spam or otherwise, should now be delivered.
This change has been rolled out nationwide and is nearing completion.
Therefore you should soon cease to receive those failed delivery notifications.
Please post an update in a week or two. If, for any reason, you continue to have issues after this time we'd like to know so that we can investigate for you.