Because as far as the email protocol is concerned attachments are part of the body, just wrapped in a multipart MIME message along with text body.

But Gmail itself may handle attachments differently.

> But Gmail itself may handle attachments differently.

AFAIK, Gmail handles attachments the same.

When it sends them, yes, but this is more what I was referring to: https://news.ycombinator.com/item?id=7842868

Any decent PGP plugin encrypts the attachments.

Regardless of how e-mail protocol transfers attachments, GMail pre-uploads files to their servers when composing an e-mail, so if you want to encrypt them, you'll need to do it beforehand.

> Why would attachments be considered part of the body?

Because if you look at the low-level structure of email, "attachments" are just parts of a body that is in multipart/mixed MIME type.

If you look that low, the body isn't actually encrypted, just the parts of it that contain your data.

Answering the GP, that varies from one implementation to another. Most clients encrypt attachments, but it looks like this one extension only encrypts the textarea contents.

Right, I was responding to the "why would attachments be considered part of the body?", not describing whether or not the Google implementation actually did treat them that way.