I found this thread after it was cross-referenced in the FAQ: Reason for flight delay thread.

Following the BA forum's advice, I took a hotel following a long flight delay that forced me to fly the next day. What is the best email address to which I send my reimbursement request? The FAQ does not provide an email.

The Germany-facing BA site provides [email protected] in its legal notice. Is that the way to go or have you had more success with another address?