[waseemsadiq]

(I used to run my own cloud based e-mail aggregator www.inbox2.com)

The primary problem with these services is that they have to pull content and have to do it regularly. That means going and checking your inbox every 2-5 minutes to be able to provide a descent experience. Your ISP e-mail provider (or gmail etc) sit there and wait for e-mail to be sent to them making it less processing intensive (push based systems).

There are some techniques such as imap IDLE to make this a bit more efficient but 1. not every e-mail provider supports that and 2. for ex. with gmail idle caps at about 35K connections per box.

You could also have for ex. gmail forward all email to a custom address but average users generally found this very confusing and couldn't get this going.

We calculated that it cost us about 2 euros per month to support a free user providing a 'good' user experience. Good luck making that back as paid service is also not a (scalable) option; the general consensus being: "email is supposed to be free" or "I am already paying for my gmail!".