I think the most easy and user friendly way for you is to use [Rules][1] module.

EXAMPLE:
Create new rule
[![enter image description here][2]][2]
Add action
[![enter image description here][3]][3]
[![enter image description here][4]][4]
[![enter image description here][5]][5]

Follow next steps to set your mail.


  [1]: https://www.drupal.org/project/rules
  [2]: https://i.sstatic.net/s8V8b.png
  [3]: https://i.sstatic.net/u12we.png
  [4]: https://i.sstatic.net/dA0dr.png
  [5]: https://i.sstatic.net/UobNk.png