Dall'Help di Gmail
What's the maximum attachment size?
With Gmail, you can send and receive messages up to 10 megabytes (MB) in size.
When you add an attachment, the size of a file may increase because transport encodings (the information that allows your message to be safely sent and read) are automatically added.
This means that in some cases, attachments that are 6 to 10MB in size may push the total message size above 10MB. When this happens, Gmail displays a warning that your message exceeds the 10MB limit.