I think I figured it out. When in File> Options> Advanced> Send and Receive, there is a Send/Receive button on the right-hand side. I clicked on it and unchecked Setting for group "all accounts" and schedule an automatic send/receive every 5 min. and that seems to have prevented automatic send/receive which is what I want. Now, I can manually send/receive when I want, but it no longer automatically sends/receives.