imapsync - Console-based utility for migrating IMAP mailboxes.
OfflineIMAP - OfflineImap synchronizes email between an IMAP server and a MailDir or between two IMAP servers.
IMAP Upload - IMAP Upload is a tool for uploading a local mbox file to IMAP4 server.
Fetchmail - The Fetchmail Project
audriga Email and Groupware migration - Easily migrate your email, contacts, calendar items and tasks to your new provider or server. No software installation is required.
IMAPSize - IMAPSize