It's an inconvenience but delete from computer browser. Not much development and support for yahoo mail systems these days. Not really a Galaxy phone problem.
it is a samsung mail problem. Emails from yahoo, live, hotmail, gmail and ymail do not get deleted from the respective servers when deleted from samsung mail. This began with the last update of samsung mail.
yes it feels it has happening from that last update now that you mentioned it , and I think about it! Any solutions to this ? I went from a computer and deleted them .. for now.