If you do block it, your access to the account you’ve created might be in jeopardy. At least it depends on how you “block” it. If the service receives an error

If you do block it, your access to the account you’ve created might be in jeopardy. At least it depends on how you “block” it. If the service receives an error on future emails, the user’s account can be disabled, as usually described in the TOS.