I agree with Patrick here.
The obfuscated login error message is a good (and often used) security measure, because giving any hint to a hacker is always a bad idea.
So please keep the "Authentication failed" message as generic as possible!
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)