Classic Mini DIY review for Auto Purchase Orders

The app provides all the features it says in a really easy to use method but I cannot get my suppliers email clients (I have 4 different suppliers) to stop sending the emails to spam. I have confirmed my email within the Auto Purchase Orders app but they still get sent to spam. Is there any way to fix this? I am about to remove the app if not, because its actually adding more work making sure my suppliers actually got the emails.