In MantisBT, there is no limit on the number of user accounts that can be created. Typically, installations with thousands of users tend to have a limited number of users that have access level above REPORTER.
By default users with ADMINISTRATOR access level have access to create new user accounts. The steps to do that are:
Click "Manage" on Main Menu.
Click "Manage Users" (if not selected by default).
Click "Create New Account" button just below the alphabet key.
Enter user name, email address, global access level (more details about access levels later). Other fields are optional.
Click "Create Users".
Creating a user triggers the following actions:
Creating a user in the database.
If email notifications ($g_enable_email_notification) is set to ON, then the user will receive an email allowing them to activate their account and set their password. Otherwise, the account will be created with a blank password.
If email notifications ($g_enable_email_notification) is set to ON, users with access level about $g_notify_new_user_created_threshold_min will get a notification that a user account has been created. Information about the user like user name and email address are provided. The IP of the user that created the account is also included.
When the 'Protected' flag is set on a user account, it indicates that the account is a shared account (e.g. demo account) and hence users logged using such account will not be allowed to change account preferences and profile information.
The anonymous user account specified with the $g_anonymous_account option will always be treated as a protected user account. When you are creating the anonymous user account, the 'Protected' flag is essentially ignored because the anonymous user is always treated as a protected user.