I need to migrate a domain (users accounts and mailboxes content only) from ServerA running "Release 6.0.4_GA_2038.UBUNTU8_64 UBUNTU8_64 NETWORK edition" to ServerB running Release 6.0.7_GA_2473.RHEL5_64_20100616202447
CentOS5_64 NETWORK edition". These servers are production holding many other domains and serving dozens of concurrent users.

1. What are the required steps to perform the job properly?

2. After the clients are moved to the new server how can I assure that they don't start downloading their old messages?

Thank you!