We try to keep the white listed IPs/Domains/addresses to a minimum. However, individual users have their own white lists to which they can add whatever addresses they want. I've forwarded your message on to the subscriber you indicated with instructions to add you to their white list if they really want to receive the email. Perhaps you should include instructions to potential subscribers to add the From address of whatever mailing list they sign up for to their personal white list, if such is available to them.