Email Services without registration

Can I send emails without registering the email id with AWS? I have deployed a app in AWS. The app sends OTP to the registered user (of the application - not AWS user). The OTP is sent to both email (as email) and mobile (as SMS). In all the samples that I have seen, AWS asks us to register a users phone number and email to a topic. But, I cannot be asking the suer to subscribe to AWS services. Since the user is subscribed to my application, and I have the users phone number and email Id, I want to send the OTP messages and other messages by email/SMS. My application is built using Java. And I need this notification services to send the messages to the end users phone ane email without them subscribing to any topics/services. How can I do this?

Thanks & Regards, ~Venki