[lzimm]

or, of course, there also exists the rebuttal that, uhh, there's no reason mailbox can't work with things that aren't gmail.....

[coldtea]

Except if, uhhh, they have made too many assumption on Gmail features being available, so that from the backend to the UI layer, it needs a good, over-through, rewrite to work with anything more standard.

[justincormack]

Gmail has spent a lot of time making it work well with web mail clients, be fast etc. Other people have not done this much in general, they would probably have to buy someone.