Why It's a Bad Idea to Send Huge Files by Email

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.

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.