从嵌套回调函数返回值

Question

我有一个嵌套的回调函数，我想从中返回值，但是很遗憾无法执行此操作，有人可以帮助我实现这一目标吗？

export const sendVerificationMail = function(user, token): boolean {
let sent: boolean = false
let transporter = nodemailer.createTransport({
    service: 'email',
    auth: {
        user: 'xyz@email.com',
        pass: 'abcdef'
    }
})
let link = `http://localhost:8080/user/reset?user=${user.email}&token=${token}`

let mailOptions = {
    from: 'xyz@noreply',
    to: user.email.toString(),
    subject: 'Your Reset Password Link',
    html: "<h1>Welcome</h1><br> " +
    "Please click the link below to reset your password<br><a href="+link+">Click here to reset</a>" 
}

  transporter.sendMail(mailOptions, function(error, info) {
    if(error) {
        console.log(error)
        throw error
    }
    else {
        console.log('verification email sent to ' + user.email + ' ' + info)
        sent = true
    }
  })
  return sent
} 

此sendVerificationMail函数为什么总是返回假值？