This is very annoying and makes me miss important email. After receiving an email, it's marked as read by the Mavericks Mail App. Anyone bumped into the same issue? Any ideas?
I had/have the same issue. With IMAP email server, if you have another computer, or phone, etc. checking mail from the same server it marks it as read in Mail. Change your settings (or remake a profile) to POP instead of IMAP. Solved for me.