When sending emails to members from CU*BASE, or any emails to members for that matter, Google, Yahoo, and likely many other major tech companies that deal with email traffic require that the email include what they call a "one-click unsubscribe" link. Having the member reply to the email or call a number decreases the delivery rates of your message and makes it more readily marked as spam. 

Simply have the link say, "Unsubscribe" and link it to an external opt-out website (that you will need to monitor).  Don’t include extraneous text such as “...and fill out our form to unsubscribe” as some ISPs consider that an indication that the email is spam.

Xtend offers a service to manage your unsubscribes at a low monthly rate.  Check out the website and Xtend store below for more details.