Following up on this question. It seems like mailchimp is the only reasonable option from my research. Am I right that mailchimp is the only email program that connects with jetpopups and jetelements? All I can find on their site is mentions of mailchimp.
https://crocoblock.com/widgets/subscribe-form/
https://crocoblock.com/knowledge-base/jetelements/how-to-set-up-mailchimp-account-mailchimp-list-id-and-api-key/#mailchimp-account-creation

So–> using one of the mailchimp alternatives would make the included plugins a lot less useful, as I understand it? I’m just confirming this before sticking myself with mailchimp as my only good option without finding workarounds. Thanks!