When are attachments transcoded in gmail?

Question

With a internet connection which charges based on data transfer (like 20 cents per 100KB), is it good to send binary content like pictures and videos by gmail or any other web based mail? I know that mail uses MIME protocol and converts binary data to base64 format which increases the size of the file by 30%. But when does it happen in case of gmail? Does my browser convert into base64 thereby increase the file size and then send(I pay more) or the file is first uploaded to the gmail server as binary and it converts to proper mime format and sends to destination server? Also what happens when I download?

How does desktop mail clients like thunderbird, evolution work in this regard? which one will save data transfer and thereby money?

Answer 1

The data is uploaded via normal browser means (binary) onto the Google servers. Then, on the server, it is converted into a normal attachment and the email will be sent.

Same for download: GMail presents you the icon for the attachment, you click it, Google extracts the original data and downloads it via regular browser means (binary).

In case of multiple attachments, GMail even offers you to download all at once and pack it into a .zip, which might reduce the overall size of the transfered data.

Desktop clients do the MIME-encoding on your desktop, thus increasing the attachment and then sending the mail. This should not save you any data/money, because that mail is actually bigger than the original data.

So, at a first glance GMail might be better in terms of transfered data, but don't forget that it has to transfer the whole UI over the wire.

Want to read a different mail? ⇒ Data transfer.
Want to re-read an older mail? ⇒ Data transfer.

With a desktop client the data is on your machine, no data transfer will be involved as long as you do not press "send".