If you send an email account using your Gmail Account and you also send the email to yourself. You will get this warning, Be careful with this message.
You don't need to be alarmed it. It will only display to your account and not all the other people in your Contact List that have a Gmail account.
To avoid it, you can send from one of our email accounts such as email@example.com and change your reply to address to be your Gmail account that way it will look like you sent it.