Depending on your Windows 2000 configuration, MSMQ can be used in a domain environment or a workgroup environment. The difference is that for MSMQ, a domain environment includes domain controllers that provide a directory service, such as Active Directory, whereas a workgroup environment does not provide such a directory service.
In a domain environment, an MSMQ network is a group of Windows 2000 sites, connected by routing links. Sites map the physical structure of a network, whereas domains map the logical structure of an organization. Sites and domain structures are independent of each other. A single site can have multiple domains, whereas a single domain can also have multiple sites. In Windows 2000, a site is defined as a set of computers in one or more IP subnets. Routing links are logic communication links created by MSMQ to route messages between different sites. In MSMQ, a computer that can provide message queuing, routing, and directory services to client computers is called an MSMQ server. A routing link is made up of MSMQ servers, one on each site.
Don't confuse routing links with site links. Routing links are used by MSMQ to route messages between sites, whereas site links are used by domain controllers to replicate Active Directory between sites.
An MSMQ computer can also run in a workgroup environment that is not part of a domain. There are several restrictions, however. All the benefits provided by Active Directory Services are not available.
First, messages cannot be routed by an MSMQ server; a direct connection with the destination server is required.
Second, you can create and manage only private queues on a local computer. You cannot view or manage public queues. You can, however, send messages to or read messages from private queues, provided that a direct connection to the destination MSMQ server is specified.
In MSMQ 2.0, public queues are those published in Active Directory and can be accessed anywhere in the Active Directory forest. Private queues are not published in Active Directory and can be accessed only by MSMQ applications that know the full pathname or the format name of the queue. Public queues are persistent. Private queues are lightweight and more suitable for offline operations in which the directory services may not be available.
Finally, you cannot use internal certificates to send authenticated messages. Instead, you must use an external certificate.