SmtpJS completely securing credentials?

Question

I am trying to send an email using my smtp server and SmtpJS. The problem is that even when using a secureToken generated on their website someone can just go to the sources, modify the destination email and practically send an email to someone pretending it's me. How can I set a permanent email address that my server can send emails to? Hope I'm clear enough. Here is the example from smtpjs.com

Email.send({
    SecureToken : "C973D7AD-F097-4B95-91F4-40ABC5567812",
    To : 'them@website.com',
    From : "you@isp.com",
    Subject : "This is the subject",
    Body : "And this is the body"
}).then(
  message => alert(message)
);

Answer 1

Try following these tutorials, preferably with a burner email account. I can't guarantee they'll work.

https://kaustubh72.medium.com/send-e-mails-with-smtp-js-a8e07e1d0b6b

https://hamzafarooq951.medium.com/send-e-mails-in-javascript-with-smtp-js-detailed-guide-5ab92cde7c49

If you manage to figure it out, let me know as I am also in the same predicament as you.