Only by those who never worked on these kind of services. Running something like a webmail service is being flypaper for dickheads. As soon as you gain any sort of popularity you will have some very hard and sharp lessons about the lengths spammers will go through to make abuse your service.

First rule of designing anything: "if some cunt can make a buck by completely fucking over your system then that cunt will completely fuck over your system because that cunt is a cunt."