In many organizations, Exchange Server 2013 is not the only product that is deployed as part of a greater unified communications and collaborations strategy. Although Microsoft offers a wide range of technologies and products that, together, can fill this need, companies often use other applications.
Describing and understanding these components is another important aspect of your architecture preparation.
First, it's a good idea to start an inventory of what other products and components are tying into your messaging infrastructure. As described earlier, this could go as far as looking at the different networking devices to multi-functional devices e-mailing unauthenticated over SMTP.
Once you ...