Preventing emails that don't exist from registering

Hi, yesterday I added some functionality to my registration function that would remove a user from the site if an error is caught after trying to run wixUsersBackend.emailUser() during the registration process. It seemed to work fine with an email I tested yesterday (although I can’t remember which email I tested) but today after trying against some emails that I can verify don’t exist no error is caught and the email seems to send successfully. Surely if emailUser() tries sending to an address that doesn’t exist it would throw an error?

This is the snippet from my registration in question:

return wixUsersBackend.emailUser('XXXXXX', reg.user.id, {
    variables: {
        approvalToken: reg.approvalToken
    }
})
.then( ()=> {
    console.log("REG STATUS ", "Wix-users signup successful.");
    return "SUCCESS";
})
.catch( (emailErr) => {
    console.log("REG STATUS ", "Error sending email.");

    //Remove user account:
    DeleteUser(reg.user.id, 0);

    return "EMAIL ERROR";
});

Why is DeleteUser() never getting called? Shouldn’t the catch block be running or is there something I’m missing?

Thanks.