I figure out what happened here.
I am using the ISPConfig Remoting Framework 1.0 library to create the accounts from a web.
It just happens that an administrator used a file for a massive user creation and this file contained "line feeds" at the end of the name.
Causing this odd-look /etc/passwd and also affecting the proper functioning of the ispconfig update process.
I also find out that no check is done for a new user to have an email already asigned as an alias to another user.
The ISPConfig Remoting Framework library creates the user, all the process work's fine, but the sendmail fails because there are repeated entries in the /etc/mail/virtusertable file.
Also this lead to an incomplete updated configuration, so mail worked fine for old accounts but "rare" for some of the new ones.
Leaving the "email" server working in a rather "extrange" mode since the virtusertable.db file is old in respect to the rest of the configuration.
I cleaned the names of "unwanted" characters and erased the repeated aliases and everything went back to normal.
Thank's again and hope this information is good for you improve the ispconfig software.