I don't prohibit them, they can use their space anyway they like. Webmail like Yahoo and Hotmail can delete or leave the messages just like Outlook. If that's all they use, they don't need to store it on the server. They have a certain amount of space, they can fill it up with email or web pages or pay for more space.
we have a different policy, they can use their space anyway they want as long as we like the way they use their space. They can post LARGE websites, with BIG files, we just don't, any more, let them keep large email files - that kills CPU performance more than anything else on our servers.
As I say, we're mean. Jale