There are advantages and disadvantages to spoofing Outlook into using its native protocol to talk to a non-native back end. On the plus side, Outlook-to-Exchange communication via MAPI relies on RPCs (remote procedure calls) as a transport mechanism, increasing the number of packets that need to be exchanged between the client and the server. The increased packet overhead makes the bandwidth for dial-up connections a real bottleneck in the Exchange world. MAPI-connector technology avoids this overhead by converting MAPI to a less-bandwidth-intensive transport on the client before it traverses the network.
On the negative side, MAPI is Microsoft's protocol. It is documented (though not well), and Microsoft remains committed to using it, not only for Outlook but also for the e-mail hooks other Office applications use. Of course, that doesn't mean Microsoft won't pull the rug out from under MAPI or change it enough so that existing products no longer
function as intended. However, because MAPI is embedded in so many Microsoft and third-party applications, this scenario is unlikely, but forewarned is forearmed.
Just the Two of Them
We tested two contestants: Stalker Software's CommuniGate Pro (CGPro) mail server and SuSE Linux's Openexchange Server (SLOX). Because SLOX doesn't yet have a MAPI connector, it lacks several crucial capabilities. For this reason, we tested both products but did not rank the pair against each other. SLOX may be missing a MAPI connector, but it does have Outlook replication technology that works well.