Install and run Kerio MailServer.
In Kerio MailServer, the IMAP service must be running on port 143 of the IMAP server.
On a machine which can access both Kerio MailServer and the source IMAP server, install Kerio IMAP Migration Tool. Kerio IMAP Migration Tool can be installed on any of these systems:
Windows (all versions supported by Kerio MailServer),
Linux[1] (all distributions supported by Kerio MailServer),
Mac OS X 10.4 Tiger and later.
The migration tool can also be installed on both the source or target mailserver.
Before starting the migration, it is recommended to make sure that the source email server cannot accept new emails temporarily. Otherwise, migrated data might be inconsistent.
The migration requires that both the Kerio MailServer and the source IMAP server are running.