@sadhakbj Years ago, I was using an on-premsis SMTP server for email relay. As you have experienced, seldom a message would not be delivered. Looking back on it now, I suspect it was probably due to some error such as "try again later" because of high volume, or some other rejection response. Since I didn't catch the error, I never knew. I also was much less experienced back then :) It wasn't long after that where I started using EWS to dish the request off to an Exchange server to handle. As soon as I made that change, I never "lost" another email.
I think what the Laravel documentation is saying is it's often easier to deal with an API as they are often well documented, fluent, simple, and provide error handling. If you get a success response, you can relax, knowing that the service will worry over failures and either resolve it with additional attempts, or notify you of delivery failure.