Users who register for Newsletters on a website will subsequently receive the Newsletter email, when it is published - all managed from the website. When set up and managed correctly, you will achieve the highest level of delivery success (ask your IT admin about the corporate SPAM filter and badly configured web servers!).
Furthermore your email system must report back to you how the email has performed. And you can then decide whether to modify things.
Our web system shows you an honest assessment of email performance. So you dont need to assume that an email has reached its destination.