Password changed or recovery options changed email
To help keep your account secure, Google sends you an email any time your password is changed or one of your password recovery options (your backup email, security question, or phone number) has been added, removed, or updated. If you made this change, you don’t have to do anything.
Notification about a change you didn’t make
If you receive a notification about a password change that you did not make, someone else might have accessed your account and changed your password. To help keep your account secure, you should secure your account.
Similarly, if you receive a notification about a change to your password backup options you didn't make, someone may have gotten into your account, and you should secure your account.
Notification about someone else’s account
If the notification is about changes to the password or password recovery options for another person’s Google Account, someone may have accidentally typed in your email address when typing in their own secondary email address. Don’t worry, being added as a secondary email address won’t affect the security of your account or your account settings, so you don’t need to do anything.
In some cases, you might see a link at the bottom of the notification email that you can click to remove your email address from the other person’s account.
Related articlesChoosing a strong password
Unusual activity alerts
Adding recovery options to your account