depending on the number of people who sign up to receive this new letter, you may run into some server limitations.
Your SMTP server will likely have some limitations on the number of email that can be sent at one time. If the number of addresses in the database exceeds this limit, those people will not receive the news letter.
Universal Email is not really intended to be used as a mass emailer, you would need to add logic to pause Universal Email after so many emails where sent, then resume sending.