@zudn - Anytime you have a form on a website it is going to get spam / bot entries - it’s all just part of being on the internet now.
Subscribe2 has 2 step subscription process in line with accepted privacy standards, enter email on form, get an email with a link to click to complete the subscription. Most spam addresses don’t actually get the confirmation email, or they don’t click the link, so the address is not confirmed and is automatically deleted after a period of 28 days.
Ensuring your site is hardened against bots in your .htaccess file or equivalent and using honeypots are good strategies. After the you kind of have to accept it is going to happen.