I run a small hosting business, and I use Plesk on AWS EC2. I cannot send emails to anyone, which in turn hinders me from sending activation emails, and it also hinders me from knowing if there is a problem.
After doing a bit of research, I found that it was a limit on the AWS instance. I filled out the form regards to releasing rDNS limits off of my instance. They simply rejected all of the requests.
I then tried using Brevo and Mail jet to fix the problem. I set up the mail relay and it simply still does not work. I do not know if it is something wrong I'm doing, or if there is another solution.
P.S. I even completed the Udemy course that Plesk offered to fix these sending issues. That still did not work.