To find the Application ID and the Application secret, please navigate to menu "Applications".
The very first row contains the information needed.
To reveal the Application secret (which is your password) you have to click on the small lock.
By clicking on the small locker next to Application secret label, you will be prompted to fill in your password:
After filling in your password and pressing <Yes, show secret> button, you will be able to see your Application secret and use it as password for your SMTP user.