Is only contact forms protected?

Coming here from https://cscrunch.com/blog/corey-pennycuff/dmarc-policies-are-eating-my-d..., which asserts:

There is a module on drupal.org that addresses some of this problem, but I don't think it goes far enough. It only protects contact forms, while my solution covers all emails.

Is that true? If so, then why only contact forms?

These are not just rhetorical questions, because this module's code looks more complete (than the offered on that blog) and I wanted to start using it, however I wonder what happens to e-mails sent from webforms or custom forms? Why not to protect all forms?