It is recommended to use “in to” instead of “into” when “in” is a verb phrase. As such, I would conclude that “opt in to” would be preferred over “opt into”, since “opt in” forms the verb phrase. I didn’t notice I copied the word “opt-in” into some other dictionary. I can see that no number () can be found in the whole Macmillan list.

What are your thoughts on this topic? Are the forms of the two kinds of comments correct?

What should I do first before committing crimes?