• Converting the user mailbox into a shared mailbox. Microsoft even provides a single click conversion (http://blogs.technet.com/b/exchange/archive/2015/02/06/single-click-mailbox-conversion.aspx)
• Put the mailbox under legal hold and remove the license.

But what if you’d rather not spend the money in the first place? You just want the data over and that is it.

Let me provide you two options that every migration tool should be able to do.

• Copy data from a user mailbox on-premise directly in a shared mailbox in Exchange online.
• Copy data from a user mailbox on-premise directly in a shared/user mailbox sub folder, e.g. Inbox/UserX

If we take a look at MigrationWiz, those options are possible.

• By defining the source SMTP address of the user and the SMTP address of the shared mailbox on the destination, the data will flow immediately in the shared mailbox without any user mailbox in the middle.
• By providing a folder mapping option, you can define the destination folder for the inbox. You define in MigrationWiz the source SMTP address of the user, the destination SMTP address of the user or shared mailbox and add folder mapping in advanced options. Read more about folder mapping on the community site here.