Gmail has increased the maximum attachment size to 25 MB in June, but some people want to send larger files. Daniel wrote a thoughtful comment that explains why it's a bad idea to send huge files by email:

People who demand large message size limits rarely understand the limitations of the email transmission.

Because of the MIME encoding used when sending binary attachments, your files expand 33% when sent via email. In other words, a 15MB attachment requires 20MB plus the message text, plus message headers.

Note, If you're able to send 20MB attachments, will not say that the user on the other site is able to receive them ;)

A 10MB mail is big enough these days...