If there is a requirement to upgrade FreeBSD to a latest version, how do we relocate user accounts, groups, home directories, mails etc to the new? Follow these steps to get it done. Copy over the following files from the old system to the new system

/etc/master.passwd /etc/passwd /etc/group

Run the following command.

/usr/sbin/pwd_mkdb -p /etc/master.passwd 

Copy all the home directories and email directory to the new system.

Source: http://www.myptsmail.com/blog/?p=72