e-newsletter: How to send out double opt-in email after registration?

Hello,

can you tell me how to send out a double opt-in confirmation email to users that registered?

Those users do not sign-up for the newsletter explicitly. Rather they either register via the WP registration form or via FB Ultimate Plugin sign-up.

I did find this thread:
https://premium.wpmudev.org/forums/topic/e-newsletter-double-opt-in-confirmation-link

But I don't know how to insert that link into a newsletter send via e-newsletter.

Hope you can help me out here!

Thank you.
Tobias