I don't agree with you Samuel, if the restriction is with his alloted space, then it isn't unlimited. There is always a limit there, wether it be financial, physical or just because current technology cant accommodate it!
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Samuel's right. You have no innate limitation on the amount of emails, etc other than the disk space and BW you choose. Someone may be able to fit 10,000 email addresses in one account, while someone else would use up their space with one.
It's like being able to take as many (unlimited) goldfish you would like from a store that you can carry. You can't carry an infinite amount of fish, but they won't limit the amount per se.