Developed by Thibaud Djian of Hoverdesk fame, EzPop is a free skinnable email/news checker.
Its main feature is to check your mail accounts every 1 to 99 minutes. When you have mail, EzPop will warn you by a mailbox image, a sound or a pop-up

MailEnable produce high performance mail server software. They even offer their entry level mail server software as freeware which is trully excellent. I use it for ALL my mail.