I sometimes send myself some notes using Gmail, but I think if it is regular email anybody on the Internet backbone or routing place can read your email, so it is not private. But Gmail uses HTTPS.
So what if I send an email to myself at Gmail, is it secure (nobody can eavesdrop it)?
And what if I send to my Yahoo or Hotmail account, or to mywebsite.com account?
When you send an email to yourself (for example [email protected] to [email protected]) using HTTPS and a web browser, the email is not transmitted out over the internet "in the open". So someone would have to compromise either your computer or the Gmail servers to read your message. However, if you send the message to a different server, such as yahoo, hotmail, or mywebsite.com the message is transmitted across the internet and potentially vulnerable to interception.
Typically no one is going to intercept these emails so if you are concerned only about personal privacy (like the details of a relationship) you don't need to worry. However, if the information is very secret, politically sensitive, or very valuable (like the password to your $5 million Swiss bank account) it is good practice not to send this information in an email because it could theoretically be compromised. A tool such as GPG can be used to encrypt this type of information, or it can be sent by another trusted method.
If you send a message inside the domain (e.g. from Gmail to Gmail), then it is processed locally, never sent outside Gmail's network.
When you send a gmail message to yourself, then anyone with access to gmail servers can read it because it doesn't use encrypted storage. When sending from gmail to other servers it is even more vulnerable because your message can be read from recipients storage space as well as intercepted during transmission.
If you want to ensure end-to-end security, then you must use services such as CryptoHeaven that use fully encrypted storage; where server administrators do not have the decryption keys and cannot read your email.
