This guide explains how you can migrate mailboxes between IMAP servers with IMAP TOOLS. IMAP TOOLS is a collection of Perl scripts that allow you to do various tasks with IMAP servers and also POP3 servers. In this article I will focus on the scripts imapcopy.pl (copies messages and mailboxes from one IMAP server to another) and pop3toimap.pl (copies POP3 messages to an IMAP server). Both scripts support SSL. If you specify port 993 (995 for POP3) then an SSL connection is initiated. If the port number is 143 (110 for POP3) then it will try a non-SSL connection. With any other value the port will be tested to see if it supports SSL. If so, SSL will be used to make the connection; otherwise a non-SSL connection will be made.
Read more at HowtoForge