For Exchange Server 2003 Enterprise, 4 storage groups x 5 stores each = 20 databases.
At the beginning of this article, it states, "Exchange Enterprise supports up to four stores per storage group, or up to 20 stores per server."
Of course, we can have 4 storage groups EXCLUDING the recovery storage group, so 4 sg's x 5 stores = 20, so the math adds up. This article says we can only have FOUR stores per group, so it only adds up if you take 4 sg's + 1 recovery sg x 4 stores, which I believe is just plain wrong. You get 5 stores per sg. People seem to love to say "don't count the recovery storage group", so I won't - you could potentially house 25 databases/stores, although the last 5 should be reserved for exactly what the name says.
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