From about 2000, the leading email product used within businesses has been Microsoft Exchange. The product was launched on June 11, 1996, replacing Microsoft’s earlier MS Mail products. Its primary competitor has been Lotus Notes.
MS Exchange is a good example of the move from PC LAN email to client/server computing that took place in from 1995-2000. With MS Exchange, servers were not limited to being passive email stores. Message servers could also do such things as searches though email stores, transfer of emails to other servers, and message store backups.
As of 1995, the leading PC-based email product was cc:Mail. However, cc:Mail’s manufacturer, Lotus Development, did not migrate the product to a client/server architecture. Instead, Lotus offered cc:Mail customers the option of migrating to the different email system provided by Lotus Notes. Most customers found this less attractive than migrating to MS Exchange.
In hindsight, this was a classic example of a vendor shooting itself in its own foot. Had Lotus offered cc:Mail customers an upgrade path to a client/server version of cc:Mail (not a hard thing to do), it would probably have maintained its leadership position. Instead, it inadvertently handed Microsoft much of its customer base.
Wikipedia has a good summary of the historical development of MS Exchange here.–David Ferris