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I created a script that uses the Sendy API to subscribe and unsubscribe users based on their membership level status if you use the WishListMember WordPress plugin:
It piggybacks off of the arpReach autoresponder service, since that one provided a customizable URL to post data to and could support the unsubscribe feature.
Note that you currently have to manually create the link yourself, but it's reasonably easy to do, and at some point I'll upload my project that let you's add things directly into the Sendy interface. This is what that looks like which makes this dead simple:
I'll try to add that project and some sample updates in the near future...need to go get dinner going now though...
Thanks for sharing this Blaine.