When you send an email, remember to determine what kind of information you are sending out.
Is it team information, important information for all members – or a newsletter?
Information
If it is information, you must uncheck the box "Respect 'no thanks to newsletter' for this message". Then ALL recipients will get the message – regardless of whether they have accepted or declined newsletters.
Newsletter
If you are sending a newsletter, you should leave the box checked. Then only those recipients who have said yes to newsletters will receive the email.