MailWasher allows you to preview multiple accounts and all aspects of your email before you download them.
It also allows you to delete and bounce e-mails back to the originator. The sender will receive an e-mail saying the address was unknown. Another feature helps identify and mark an e-mail as normal, a virus, possibly a virus, potential spam, probably spam, a chain letter, and blacklisted, so you can deal with the e-mail as you wish. Other features include customizable filters, use of MAPS RBL to identify spammers, multiple accounts, visual and auditory notification of new e-mail, minimization to the system tray, and much more. It is compatible with POP3 servers.
Will only monitor one email account. A Pro Version is available without restrictions.