Spam is one of the most discouraging things about managing a WP User Manager membership site. It is possible to block users from registering on your site by either defining specific email addresses to block, or entire domains. For example, block all users with @hotmail.com email addresses.
This functionality is included with the Security addon.
Block Specific Email Addresses
Navigate to Users > Settings > Security and scroll down to the ‘Block List’ setting.
There you can enter the specific email addresses, using a new line for each email address.