Anyone considering SmtpJS (whether in an Airtable product or anywhere else) should think carefully about the privacy implications. The library operates by sending your message to the owner of smtpjs.com, who apparently sends an e-mail on your behalf. You’ll have to trust that they respect your privacy, though it’s concerning that their website makes no claims about how they use your data.
That said, it’s still worth discussing this approach because it’s an opportunity to learn about the Scripting Block and web development in general.
The Scripting Block does not support JSX, so to output information, you’ll have to rely on the API methods it provides for this purpose. The Scripting Block’s documentation is available here.
The task of sending e-mail is unrelated. You may be able to use SmtpJS, but because your script must be fully self-contained, you’ll have to copy and paste the library’s source code.
This may not work, though. The Scripting Block’s environment is not the same as the typical web browser environment for which SmtpJS was likely designed. The project’s documentation is minimal, so it’s hard to predict whether or not the library will function in this context (or whether it will continue to do so in future releases).