When trying to login via the web interface and getting blocked due to wrong username/password SmarterMail will block the IP address and not the account. That is why you were not able to login to a different account. The settings for this is handle in the webconfig file under the MRS folder. The lines you will need to change if you are planning on modifying this are below.
<add key="Login.BruteForceDetection.TriesBeforeBlock" value="10" />
<add key="Login.BruteForceDetection.BlockTime" value="5" />