Bart De Vos shared a link to the SE newsletter page:
Oops! He shared his confirmation link.
I got the message: "Thank you for signing up for the Stack Overflow Newsletter! You will receive the newsletter every Tuesday." which is a little confusing as it subscribed him, not me.
I then proceeded to sign him up for the Christianity and German Language Newsletters by clicking the 'Subscribe' button after opening up the link in a private browsing window.