Great to hear you got in to the Mail tab. Regarding the From email address, this is the plugin author’s rationale for the error message:
Why does the email address in the From field have to belong to the site domain?
For example, if a mail had “[email protected]” in the From field, but was actually sent from your web server (it’s not yahoo.com), it would be highly possible that relaying mail servers consider it as a spoofed address. If you use an email address in the same domain as the site, you can reduce the risk of being treated like that.
You can disable the configuration validator by adding:
define( 'WPCF7_VALIDATE_CONFIGURATION', false );
to your wp-config.php, or adding: