One of the fundamental challenges in managing an e-mail system is making sure that e-mail continues to be accessible during big disasters like hurricanes, earthquakes and tornadoes - but also during more common disasters like a burst water pipe on the floor above your server room. E-mail has become so critical to most of us that even minor disruptions of 15 or 30 minutes can cause major problems in business continuity.Among the many products available for maintaining e-mail continuity in Microsoft Exchange environments is MailShadow from Cemaphore Systems. MailShadow provides a simple solution to the problem of e-mail continuity: it replicates individual mailboxes to a second Exchange server that operates as a disaster-recovery server. Because it updates each mailbox in real time, if the primary Exchange server fails the system can switch users to an up-to-date copy of their mailbox to continue their work, typically in less than 10 minutes. After recovery of the primary Exchange server, the recovery server will replicate information back to the primary so that the content of the two is re-synchronized.Because MailShadow uses a transaction-based replication model, it consumes much less bandwidth than some other replication systems. Also, MailShadow can use primary and recovery servers that operate different versions of Exchange and different patch levels.MailShadow\u2019s approach is interesting because it permits individual mailboxes to be made more or less disaster-proof, allowing an organization to ease into disaster recovery slowly instead of migrating all users at once. It also allows an organization to selectively implement disaster recovery capabilities, since some users just might not need 24\/7 access to e-mail. MailShadow would also make an interesting, value-added offering for managed service providers that offer Exchange hosting for smaller organizations. It\u2019s an offering that certainly is worth a look by those charged with maintaining the continuity of Exchange environments.