Answer is: Summer 14.
Attach Larger Files, Up to 25 MB, to Objects We’ve increased the size limit for attachments to objects from 5 MB to 25 MB. Collaborate more easily with larger attachments to cases, accounts, orders, and other objects. Attachment limits in Salesforce Knowledge remain unchanged. Receive Incoming Emails of up to 25 MB We’ve increased the size limit for incoming email messages from 10 MB to 25 MB, making it more likely that you’ll receive even long messages with multiple attachments in their entirety. The 25 MB per message limit applies to the entire message: the headers, the body, all attachments, and the encoding. This limit increase applies to all incoming email messages, including those that come in through Email to Salesforce, Email to Chatter, and On-Demand Email-to-Case.