AD migration

Hi

using Quest Migration manager for AD/Exchange,  Is it possible to migrate AD groups users contacts  from an source forest to target forest leaving mailboxes still in exchange org source domain. ( I know this is possible wit Quest ) 

But is it also possible to migrate mailboxes from source forest to office 365 and having migrated users in Target Forest can access their mail boxes in Office 365 so that we can decommision exchange org in Source Forest

Best Regards

Eric Kro