Sylpheed

Sylpheed is a completely free and open source email client to keep track of all your emails without you getting overwhelmed by them.

This email manager stands out for handling your system resources well – which is ideal if you don't have a very powerful computer.

It supports POP3, IMAP4, SMTP, and NNTP. It also includes search features and tools to fight spam.

Although it was originally developed for GNU/Linux, Sylpheed adapts pretty well to Windows environments too.