In the Daily Drill Down “Understanding Exchange 2000 Server instant messaging,” I showed you how instant messaging (IM) works. Before you can deploy it on your network, however, you should do a little bit of planning. In this Daily Feature, we’ll look at some of the issues you need to take into consideration.

Building around your users
There are a number of considerations when planning an IM deployment, most of which depend on the size of your organization, network configuration, and the number of users who need IM services. The first decision you need to make is whether or not you need to implement routing servers or whether a single IM home server will suffice. Each home server can handle approximately 10,000 online users, and each routing server can handle about 20,000 online users.

It’s important to note that this doesn’t mean you’re limited to hosting 10,000 users per home server. Rather, it means that up to 10,000 users can be online at any particular time for a given home server and that a routing server can handle two home servers at maximum capacity.

Also, you can use multiple home servers without a routing server. This means, however, that outside users must know which server hosts a given user and specify the FQDN of the server for the user. For example, assume you set up two home servers, and, without a routing server. To connect to another user, you must specify the server in the IM address, such as, when attempting a session with that user.

You can simplify the process by giving each IM home server a logical name, such as and If you know that a person works in the West Coast office and his e-mail address is, you can deduce that his IM address would be

Network layout issues
The next consideration is how the IM servers will fit into your network, whether inside your firewall, in a DMZ, or connected directly to the Internet. There are no IM-specific issues to consider here, as you should protect your IM servers the same way you would your other servers. If your Web servers reside behind a firewall, for example, so should your IM servers.

A fourth option is to place the IM routing servers or home servers behind a reverse proxy server, which accepts IM traffic from the Internet and relays it to the IM routing servers (or IM home server) for processing. Outgoing IM traffic goes through a separate proxy server. Generally, reverse proxy servers are used in place of a firewall rather than in conjunction with one.

Regardless of the topology you choose, IM home servers should be located close to the users they serve. For example, if you have two divisions, one on the East Coast and one on the West Coast, each should have its own IM server. Whether you use routing servers or not depends on the size of your network and the number of users you need to support for IM.

After you decide how many IM servers you need, whether or not you need IM routing servers, and where each server will be located in relation to your network and the Internet, you need to consider DNS. You must create an SRV resource record in the domain and point it to the IM routing server, if used, or to the IM home server. If you are deploying multiple IM routing servers, you need to create multiple SRV records, one for each server. Each record will have the same host name but specify the unique IP address of the server. The DNS service will then process the entries in round-robin fashion, which provides load balancing.

It’s likely that you already have DNS set up for your domain and only need to add the additional SRV records to support IM. If you don’t have a DNS server set up yet to service your domain, or your DNS zone is hosted elsewhere, you’ll have to set up the server or contact the administrator for your zone to have the necessary resource records created for your domain.

Domain structure implications
You also need to take into account your domain structure when planning an IM deployment. Although you can install Exchange 2000 Server and IM on a domain controller, you should do so only in cases where you support a relatively small number of users and the server is not overly taxed. It’s a much better practice to use domain controllers exclusively as domain controllers and host other services such as Exchange on member servers, particularly as the number of users in a domain increases.

Privacy considerations
Lastly, you need to consider how IM affects your users’ privacy. The IM client, by default, publishes each user’s online status. In some cases, users might want to hide their status from all other users. In other cases, users might want to hide their status only from specific users but allow online status notifications to be sent to others.

Each user can configure his or her settings separately to define the users who can and cannot see his or her online status. The user can also view which contacts have added his or her IM address to their contact lists and configure the IM client to notify the user when other users add him or her to their contact lists. In the IM client, choose Tools | Options to open the Options dialog box, and then click the Privacy tab to configure these options.

Just because Exchange 2000 supports instant messaging doesn’t mean you should just blindly turn it on and let your users loose. You need to take a few things into consideration first. After your network and users are ready, then you can set up instant messaging on Exchange 2000 and put your users to work.