Thanks for all of the above answers. But I have personally used a third party software to export Office 365 mailbox emails to PST. Ultimately I got the expected results. The tool has exported the bulk mailboxes to PST which saves a lot of time for me. Addtionally, there advanced features also...
Thanks for suggesting the different tools. I have picked the above-discussed tool to migrate Google Apps to Office 365. But now I want to how to perform Exchange Online move mailbox to another user easily?