We are making a change to allow customers to migrate larger mail messages to Exchange Online. We now allow messages up to 150MB to be migrated to the service. The change is available immediately to all customers and is published as a new limit in the Exchange Online limits page in the Office 365 service description. We are not changing other limits such as mailbox size or maximum send/receive limit for messages. This change enables customers with large messages to easily migrate their existing content to the message.
Source: http://blogs.office.com/2015/01/12/whats-new-december-2014/
Until later,
Henrik Walther