Gmail might be fine for basic email purposes, but it should not be counted on for any sensitive correspondence. Here are a couple of articles:
"Why do we let this creepy company spy on our emails?"
("Google does use the content of your emails for commercial gain. It scans your words and searches for key words in the same way it does when you use the Google search engine...Whatever precautions you take, anyone signing up for a Gmail account must trust that Google won’t use the sensitive, revealing information contained in the emails you send and receive for any other purpose.")
Gmail Is Too Creepy
("The powerful searching encourages account holders to never delete anything. It's easier to just leave it in the inbox and let the powerful searching keep track of it. Google admits that deleted messages will remain on their system, and may be accessible internally at Google, for an indefinite period of time...For the first time in Google's history, the language in their new policy made it clear that they will be pooling all the information they collect on you from all of their various services. Moreover, they may keep this information indefinitely, and give this information to whomever they wish. All that's required is for Google to "have a good faith belief that access, preservation or disclosure of such information is reasonably necessary to protect the rights, property or safety of Google, its users or the public.")
In short: Gmail messages are NEVER deleted--Google owns them forever. And they scan your messages for keywords. And their policy states they will divulge your data when they feel a need to--your "private" correspondence is NOT private, and Google WILL throw you under the bus!
"Why do we let this creepy company spy on our emails?"
("Google does use the content of your emails for commercial gain. It scans your words and searches for key words in the same way it does when you use the Google search engine...Whatever precautions you take, anyone signing up for a Gmail account must trust that Google won’t use the sensitive, revealing information contained in the emails you send and receive for any other purpose.")
Gmail Is Too Creepy
("The powerful searching encourages account holders to never delete anything. It's easier to just leave it in the inbox and let the powerful searching keep track of it. Google admits that deleted messages will remain on their system, and may be accessible internally at Google, for an indefinite period of time...For the first time in Google's history, the language in their new policy made it clear that they will be pooling all the information they collect on you from all of their various services. Moreover, they may keep this information indefinitely, and give this information to whomever they wish. All that's required is for Google to "have a good faith belief that access, preservation or disclosure of such information is reasonably necessary to protect the rights, property or safety of Google, its users or the public.")
In short: Gmail messages are NEVER deleted--Google owns them forever. And they scan your messages for keywords. And their policy states they will divulge your data when they feel a need to--your "private" correspondence is NOT private, and Google WILL throw you under the bus!