It would appear that your email account was hacked at some point and the rule set up.
You need to delete the rule after having noted what the rule was set to do. To do that log onto your BTMail account using a browser, not an email client/app, and then click on your username at the right hand side. Select "Settings" then go to the left hand side and select "Mail". Scroll down and click on "Rules".
This should show a list of any rules that have been set up. If you look at the right hand side of the rule you will see a Bin Icon. Click on it and verify you want to delete it.
After you have done that you will get a yellow pop up warning that the rules have been altered. You can not stop that warning which will be displayed for a few days every time you log onto your account.
As regards deleting the email addresses. If you hold down the shift key then select the first email address and while still holding down the shift key scroll down the list using the scroll bar at the right hand side and select an the email address further down the list and tick it. When you release the shift key all the email addresses in between those that you ticked will be selected. Then go to the "More" button in the menu bar and select "Delete".
Have a read through this link and sub links and follow the advice given.
How can I tell if my email account is no longer secure? | BT Help
