@jason hendriks
No, my smtp port number, password, etc, were entered correctly, but WP Mail SMTP was not able to deliver the mail because it does not have the needed feature of authenticating with the client ID and client secret.
IMO, Contact Form 7 should mention the possible necessity of an SMTP plugin in an upfront manner in its help section and general description, so that people can quickly move to this possible solution instead of being given the impression something is broken.