Brief Preface: User authorization is the very first need of every application security. In reference of operating system, OS provides password protection and keeps these file on a centralized system. Same is happens with mail clients that it also have password protection and log-in system for its user. Lotus Notes is a big platform as compared to other mail clients and business collaborations. Lotus Notes mail client is also have in-built user authentication system. By using term 'User Accounts ' I only means for a simple list of the authenticated user and their passwords records which are allowed to use that system.
Every System has some kind of user authentication with security purpose. Lotus Notes requires user name and one password for user authentication. User Name and password are stored in a file by the Lotus Notes. This file is known as USER ID file. The User ID file is saved with the extension of ".id" and known as user.id file.
It is nothing but it is simple file which is mostly used by the user of Lotus Notes. This file keeps user account information like its user name and password. This file also has some additional things as follows:
At time of notes configuration Lotus Notes Administrator offers user to give a desired user name and same time Notes provide a provisional password, which can be used further for user authentication process.
This file is stored by the Lotus Administrator anywhere on the local system. Generally it is stored in "LotusNotesdata" directory on the c drive of local system and User can save it anywhere on the Local system. It is moveable.
When user is trying to login then the software opens the last used user id file and asks for the password. After entering the password the Lotus Notes administrator compares the saved password and given password by user at that time. If both are same then the user is treated as authenticated user of Notes. User cannot interact with Domino server with the same method because it is different for the Domino server level and as local mail client application.
So the user.id file is only a data file which has only the user information and some certificates related to that user. It can be copied and saved by the user anywhere on the local machine.