Have a read through this link
https://www.bt.com/help/email/email-security/how-can-i-tell-if-my-email-account-is-no-longer-secure
To sign out of your email on a device that is using an email app you will need to nter the app's settings and either untick the box marked " automatically logon" or remove your password.
Before changing your password log onto your email account and check there are no "fowarding" email addresses or "rules" set up.
To do that click on your usernameat the top right and click on "settings" then go to "mail" at the left hand side and click on "Forwarding" and "Rules".
You should also advise your banks etc if you use online banking.
To change your password see this link.
I need to change or reset my BT Email password | BT Help
