Group - Added (by Email) - how do i prevent this?
Added (by Email) is normally added when a contact is added to the group using a subscription URL provided in any mail.

It is basically used to know how a contact was added to the group.  This information is stored in civicrm_subscription_history table(method column) in civicrm database.

If you want to simply remove Email method from your DB, you can do it by a simple SQL -

UPDATE civicrm_subscription_history SET method = 'Web' WHERE method = 'Email'


To avoid it in future, you can proceed in writing an extension and a post hook which updates civicrm_subscription_history after a group contact is created.