Two things to notice.
1. The original server was working in spite of these four entries missing in the passwd file, even for the four users.
2. Came to notice it, only after migration to new hardware, and these four users complaining that they were not able to access their mail and files.
The users were created the server-manager and not any way else.
Will confirm about the LDAP contrib, I am not sure about it.
For the time being I used the signal-event user-create command to add these users and now they are able to access their files.
thanks
Veeresh