Most of the fax servers I reviewed are fully functional products with loads of features and value-added functions. However, at some time you may want to customize a fax server to address specific business needs. For example, you may want to integrate fax capabilities into your order entry application. Maybe you want to generate a series of faxes based on information in your customer database. In some cases, you'll be able to address these needs with your fax server's high-level interfaces, such as DDE or print-stream support. In other cases, however, you'll need to introduce fax capabilities into new or existing application programs.

There are several approaches to this task. For one, you can obtain SDKs from Brooktrout and GammaLink, the fax-adapter manufacturers. However, these kits function at a low level. They let you put ASCII-text or fax-image files on a queue and monitor them, but that's about it. For another, you can purchase a third-party SDK, such as the one from Black Ice Software, but this approach doesn't let you integrate your application into your existing fax-server software. In other words, you end up with two unconnected fax applications that compete for a common resource--the fax adapter--but don't share common control or administrative tools.

A better approach is to use an API kit that allows you to integrate your application into your existing fax-server environment. Fortunately, all the fax servers I reviewed support a separate API kit to accommodate this level of customization. You can use these kits to develop C, C++, or Visual Basic (VB) programs that can take advantage of most--if not all--of the features available in the fax server. Unfortunately, none of these vendors includes the API kit with the fax server. You must get it separately. Global Village, Optus, and RightFAX provide the necessary files for free. The other vendors charge for them: Copia's kit is custom-priced; Omtool's kit lists for $1495, and Zetafax's kit is $745.

There are no international or de facto standards that apply to fax-oriented APIs, so the different vendors' API kits offer different levels of functionality. If you know that customization is in your future, you should take a close look to see how each vendor's API kit addresses your projected needs.