Snippet is:

  - name: Create root alias
    action: lineinfile dest=/etc/mail/aliases regexp="^root:" line='root: isunix' state=present
    notify:
    - new aliases

Error is:
ERROR: Syntax Error while loading YAML script, s10_mail_fix.yml
Note: The error may actually appear before this position: line 10, column 73

  - name: Create root alias
    action: lineinfile dest=/etc/mail/aliases regexp="^root:" line='root: isunix' state=present