It makes no difference whether you send from your email or via Amazon’s email system.
It will go through their servers anyway. So if the customer is opted out, it will be bounced.
If the email is important, then use the option “Additional information required”.
There is no need to write the word important in the message when doing it this way.
The only time that you need to do that, is if sending an email from your own email. But not in the message, you add the word to the subject line.
I agree with the original poster though, their email system is simply not fit for use!
It’s so frustrating trying to contact customers, particularly when trying to arrange delivery, that they simply don’t get the email or it goes in the spam folder.
Amazon simply send FAR TOO MANY emails, which is why so many get marked as spam!