With the number of bots increasing all the time, it’s likely you are aware of the problem. Unfortunately, this has a knock on effect for your integrated systems. Your email marketing mailing lists can end up populated by email addresses that have no value to you as a business but push your subscriber numbers into the next pricing band.
If you’re bothered by Russian casino reviewers or the like ending up on your customer lists and the ensuing skewed reports of disappointing open rates and click through, it’s worth looking at how you can avoid further spam submissions as ongoing manual deletion is far from an ideal approach given the time it consumes and the risk of losing genuine subscribers through misidentification.
There are a number of infrastructure solutions available to eradicate spam subscriptions to your mailing list. One approach - blocking specific IPs or blocking site visits from entire countries, both are which are perfectly valid provided there is no chance that compromises traffic from markets you sell into. A more popular solution is to use Google's reCaptcha forms, which add an extra step of verification that identify form submissions as genuine.
All Magento 2 version include reCaptcha as standard while modules to extend the functionality of Magento 1 are available. As a set of standardised forms, increasingly familiar to web users, reCaptcha provides an intuitive and robust way of verifying submissions as genuine human users.
Magento 2 has a solution with Google recaptcha