If you are not familiar with modules, check out Ansible - Getting Started with Modules.

The mail module can be used to send email. In this example, an email will be sent to john.doe@example.com. This assumes that the control node (in this example) is configured to be able to send emails using SMTP server smtp.example.com, and that the SMTP server is using port 25 to send email.

---
- hosts: localhost
  tasks:
  - mail:
      host: smtp.example.com
      port: 25
      from: "no-reply@example.com"
      to: "John Doe <john.doe@example.com>"
      cc: "Jane Doe <jane.doe@example.com>"
      subject: Example Subject
      body: "Line one \n Line two \n Line three"
...

When running this on a managed node, you may need to use delegate_to to have the email sent using the control node (that's your Ansible server).

---
- hosts: all
  tasks:
  - mail:
      host: smtp.example.com
      port: 25
      from: "no-reply@example.com"
      to: "John Doe <john.doe@example.com>"
      cc: "Jane Doe <jane.doe@example.com>"
      subject: Example Subject
      body: "Line one \n Line two \n Line three"
    delegate_to: localhost
...

Often, an SMTP server is configured with some type of security, such as starttls and authentication. In this scenario, the secure, username and password keys can be used.

---
- hosts: all
  tasks:
  - mail:
      host: smtp.example.com
      port: 587
      secure: starttls
      username: your_username
      password: your_password
      from: no-reply@example.com
      to: "John Doe <john.doe@example.com>"
      cc: "Jane Doe <jane.doe@example.com>"
      subject: Example Subject
      body: "Line one \n Line two \n Line three"
    delegate_to: localhost
...

If the email is successfully sent, the play should return the following.

PLAY [all]

TASK [Gathering Facts]
ok: [server1.example.com]

TASK [mail]
ok: [server1.example.com -> localhost]

PLAY RECAP
server1.example.com   : ok=2  changed=0  unreachable=0  failed=0