@Ezen 

I’m not familiar with email options that will add people in different lists. But there is option for sure that can add properties to people and then depending on the properties you can add them to different segments.

So instead of list create 3 segments with definition of properties from the campaign. 

You will have 3 buttons for example creating 3 different properties to people and then you use them to create the segments.

Here is more info on how to do this https://help.klaviyo.com/hc/en-us/articles/115005255248-How-to-use-links-to-collect-information-about-your-recipients

@Ezen short answer is, this is not possible and I think not allowed either by Klaviyo unless you're doing some custom coding work.

What you could do though is use the list signup form and add the following to the signup form link

?email={{ email }} which will auto fill the email form. They then only need to press signup.

But I think this is not where you're after so I'd say adding a custom profile property and segmenting based on this would be best way to go here.

Regards,

Omar Lovert // Polaris Growth // Klaviyo Master Platinum Partner

So if a second list was created and all active users were added to that list with an option to unsubscribe from that second list, is that allowed?

​​​​​Using ​@Ezen ‘s example:
When users sign up for the mailing list, they sign up with Business 1 and are added to two separate lists:
List 1A & List 1B
Therefore they will receive emails from both segments 1A & 1B (assuming separate campaigns are created for those lists).

But if someone only has interest in content relating to 1A or 1B, they could simply unsubscribe from the second list without affecting the first. Is that allowed/normal process?