Rather than using traditional opt-ins, companies like neverbounce offer real time email verification. I first saw it on the freedom platform. What do you think of it?
here is an example: click on the video and it will ask you to enter your email.
https://freedomplatform.tv/professor-david-miles-cbe-extraordinarily-costly-why-lockdown-2-0-could-plunge-uk-into-double-dip-recession/