The BT Yahoo! e-mail service is changing its terms and conditions.
From 17th June e-mail accounts that have not been accessed for 150 days will be deleted. The clock started ticking on 18th January 2013.
Polling via POP3, using web mail or if you have an auto-forward set-up all count as using the service, and reset the counter.
IMPORTANT: The accounts are not simply locked, but contents (including contacts) are deleted once the account goes past the 150 days of inactivity.