Email service providers continue to push the upper limits of allowed attachment size. Currently both Gmail and Yahoo supports attachments up to 25 MB in size, but people want more. Why do email service providers limit the attachment size when everything else such as bandwidth and disk space is virtually free? Because the mail protocol wasn’t created to handle file transmission. As a commenter on Google Operating System explains, sending large files through email is a very bad idea.
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.
When you carbon copy 20 of your friends & coworkers, a separate message is sent to each. 20MB x 20 = 400MB. That's half a freaking CD.
If 5 of those friends are on the same small company email server, downloading those messages saturates the entire bandwidth of their T1 data line for nearly 9 minutes. Because each message has separate headers, it isn't easily cached and gets completely downloaded by each recipient.
Compare this to uploading the same attachment to a web server, FTP server, file transmission service like YouSendIt, or video streaming site like YouTube. One copy is uploaded. The download is typically 8-bit so minimal expansion factor. The small business' network can cache the content, so it's only downloaded once then fetched locally from the web caching server.
Bottom line, sending a large attachment via email is relocating using the U.S. Postal Service as your moving company. It is painful, limited, and expensive.
When the file size is anything over a few Megabytes, the best way is to upload it to some free file sharing service. But for the technologically illiterate people, even that is too much to ask for. For such users there is PodMail – a free service that lets a user to send and receive files of unlimited size through email. PodMail is very easy to use and integrates with your email. Sending files through PodMail is just like sending attachments.
Update: PodMail is no longer available