I am having zimbra 6.0.8 FOSS edition & trying to migrate the all users account along with mail box in new zimbra 7.0 server using zimbra migration wizard which is newly available in zimbra 7.0
i am able to sucessfull migrate the users account in to the new system but when i am trying to migrate the mailbox using imap protocol with clear text option zimbra show me task fail when i had check the mailbox.log its give me following error

[ImapServer-54] [ip=;] ProtocolHandler - I/O error while processing connection: javax.net.ssl.SSLHandshakeException: Received fatal alert: certificate_unknown

what would be the reason for the same & how to resolved the same

Prasad Pimple