At my last employer, I helped many people do just such a thing ;)

We started by gathering requirements and understanding the business
tolerances for email availability.  We went from there to making that more
granular and then formulating a solution that met the requirements.  Worked
out quite well and included many different levels of solutions depending on
the business need.  "Dial-tone" recoverability, clustering, backups,
geographically replicated data, etc.

Al