When you move mailboxes from Exchange Server 2003 to Exchange Server 2007 you will end up with Legacy Mailboxes.
To convert these mailboxes you need to run the following command in a Exchange powershell window:
Set-Mailbox -id <mailbox alias> -ApplyMandatoryProperties
If, in the process, you get this error:
“Set-Mailbox : The operation could not be performed because object ‘<alias>’ could not be found on domain controller ‘<FQDN of domain controller>’.
At line:1 char:12
+ Set-Mailbox <<<< -id <alias> -ApplyMandatoryProperties”
That might happen because you are running the command in a Domain Controller not of the same domain as the mailbox owner.
In that case, you should run the command in a Domain Controller of the mailbox owner domain.
For that you can use these commands:
$adminsessionadsettings.defaultscope = “<Mailbox owner domain>”
$adminsessionadsettings.preferreddomaincontrollers = “<Mailbox owner domain domain controller>”
After that. just run the first command again.