I've got three POP accounts, and as far as I've ever been able to tell their default behavior is to retain all mail received until I delete it from my server either manually or automatically via a Mail > Prefs > Advanced option.
In fact, I frequently use my POP accounts to store mail that I've already d/l'ed.
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
