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.

- 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.

- 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