According to an interview given to The Telegraph, BTinternet's email services are being moved to BT-Mail following hacking claims.
This will doubtless impact on deliverablility of mail to @BTinternet.com addresses, exactly how remins to be seen.
Yahoo! are still handling mail for BTi as of this morning (10th June):
# host -t mx btinternet.com
btinternet.com mail is handled by 1 mx.bt.lon5.cpcloud.co.uk.
btinternet.com mail is handled by 10 mx-bt.mail.am0.yahoodns.net.