Hi @margaux1803, 

Welcome to the Community!

For the last two years, users have been able to self-serve opt-in preferences. However, before, this option wasn’t available to free account and you had to write into support for your request.

However, there isn’t an option to disable double opt-in via an account level, you will need to do this in each Lists’s settings option. I’d check out this interesting thread from one of our Champions on considering double opt-in vs single that might be insightful for you! 

 Thanks for participating in the Community! 

-Taylor