2 You can send and receive up to 150 MB messages between Office 365 users (where the message never leaves the Office 365 datacenters). Messages that are routed outside of the Office 365 datacenters are subject to an additional 33% translation encoding increase, in which case the maximum message size is 112 MB. You can send and receive up to 150 MB messages between Office 365 users (where the message never leaves the Office 365 datacenters). Messages that are routed outside of the Office 365 datacenters are subject to an additional 33% translation encoding increase, in which case the maximum message size is 112 MB.