I've a similar problem. I've switched it off for new mail but it's active for replies. How do I stop it totally?
There is only one option for all messages - new one and replies - available.
You can turn it on and off in the "per account" settings:
Long press on account name - Options and folders - Composing and sending - BCC to self - check/uncheck the default address (your account). There is also an option to enter a specific address. If you do not want this bcc mails anymore pls. make sure to delete also this specific one.