A friend of mine is up late pretending to be system administrator because some bozo decided their office should run an in-house mail server, and today an update hosed everything. Let’s say this shop has 15 email accounts, and a hosted plan runs about 50 dollars per user per year. Just today, the loss of billable hours, technical support costs, and system downtime makes 750 dollars a bargain, not to mention the initial investment and ongoing maintenance costs. Unless you’re a special snowflake with totally unique email needs, don’t host your own email.
(Confession: I host my own email.)