Thanks for your reply Bruno Rendeiro.
Yes, we have configured OutSystems to send emails. We have lots of apps sending emails. We have not been using emails in React or mobile apps. All our apps are using a traditional web app to send email, even if the app which needs to send email is React or mobile.
But, with that said, some emails sent via the mobile app did work. However, worked when I was running the app with the debugger active. When I preview the app in the browser or on my phone, the email doesn't work at all.