I too have real problems with BT mail, it is a real botched job because Yahoo is compromised and BTs own email system doesnt work properly.. A bit of a snapshot for BT who as a company are going down the tubes trying to save money and not really understanding their role in the modern world
I did not know this could happen but had 'lost' some emails which i have now found where you described and it is helpful for people to spread this information.
I subscribe to BT tech experts who help with general computer probs as well as BT services and find it useful at £10 per month as the staff are helpful and knowledgeable compared to BT customer service
Sorry couldn't be more helpful