Hi FDB,
Which plan are you using? Plan P or Plan E.
If you are using plan E and have enabled "Litigation Hold" for your mailbox, all data in your mailbox will be permanently preserved. Administrators can use Multi-Mailbox Searches to search your mailbox for original and modified versions of a mailbox item. More detailed information related to "Litigation Hold", see this link: http://social.technet.microsoft.com/wiki/contents/articles/9667.office-365-exchange-online-mailbox-litigation-hold.aspx .
To back up your online mailbox data, you can enable archive mailbox for your online mailbox. After enabling archive mailbox feature, you can create a custom retention policy to automatically archive data in your online mailbox to archive mailbox.
Regards,
Jacky Ding
