How do I access the user email? I am using Drupal 8 to create a website for training purposes. The user roles are Trainer, Trainee. I have content type session where I get to allocate the trainer for a particular date. It is done by user reference.

By using rules I want to sent notifications to the trainer regarding the scheduled session. But I am not able to achieve this.

Is there any other way I can sent notifications to the trainer other than using Rules module? Please help.
I am not sure if you can send a mail without any custom coding, but you can definitely do this via custom code.
Refer examples module, which has an example on how to send mail.