Create mailbox using dirsync

Hello, I go to use dirsync to create a sync users and password, the users are created ok on office365, I assign the license, and a message is showing says that the mailbox do no to be created until start a migration.

I have exchange 2007 but I do no go to make any data migration because my users use PST, I need that dirsync create the user, I assign the license and the mailbox be created.

Thanks for your help.