Until now, the maximum email size in Office 365 was 25 MB. If users wanted to ‘send’ larger document they could store the file in OneDrive for business and email a link to it.
From April 2015, the maximum possible email size has been increased to 150 MB to allow direct sending of larger messages, however existing mailboxes will initially retain their current values.
The default maximum message size for the organization can be increased and this will apply to all new mailboxes, but existing mailboxes will need to be manually edited to change their maximum message size.