Pritesh Singh asked whether anyone other than the intended recipient can view files attached to a Gmail message.
Unless you take special precautions, nothing you send by email is secure. That's doubly true with Gmail, since Google uses the content of your messages to target advertising.
I very much doubt that Google employees are reading your mail; there are cheaper ways to get the job done. But the potential of abuse is always there. And let's not forget the NSA's enthusiasm for sticking its nose into everything we do online.
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Giving up Gmail won't help much. All email, by its nature, is insecure. Your unencrypted message will go through several servers between you and the recipient. Even if the message leaves your PC encrypted with SSL (as happens with Gmail), that only protects it for the first leg of its journey.
There's no technical reason why we can't all have full, end-to-end encryption built into our email systems. A free, open-source standard already exists: OpenPGP. All it needs is universal acceptance by the major email clients and providers.
But that's not going to happen. While it would be wonderful for most of us, such acceptance would not be in the interests of Google, Microsoft, or the U.S. government.
So what can you do?
The most obvious tactic is to keep sensitive stuff out of email. You can send most messages without privacy worries. But when you want to make sure that the cops, the crooks, or the corporations can't read it, use encryption.
That's not as easy as it sounds. Your recipient will need compatible software and possibly your password. And they may not be as tech-savvy as you.
In my experience, the best method is to skip email altogether and use a service called Sendinc. Both you and your recipient will need your own accounts (free ones are sufficient for most people). You don't need to know each other's passwords; although both of you should have strong ones.
For more on how the service works and how it secures your information, see its How Sendinc works page.