Eclarsys PopGrabber is a simple program which retrieves Emails from POP3 accounts and forwards them to any SMTP Server.
COMPLETELY FREE 3 ACCOUNT VERSION available for download.
Works a a Windows service. Small .Net based program.

Please note: Current version does not support SSL connections, SMTP authentication or catch-all mailboxes (each POP3 account is forwarded to a single SMTP account). These features are planned for the next release.