I am sorry your email address has been accessed by someone else. It actually happened on the 3rd December and authenticated SMTP login was used to send a quantity of spam emails. This is nothing to do with the emails being in house and more to do with spammers knowing your email address and password. It looks like the correct account was locked from our logs. We wanted to let you know and to advise you to follow the information here What do I do if I think my email account has been accessed by someone else?
Hopefully though you have done that already as currently we see no further transgressions.