Why is there no alternative webmail of the caliber of gmail? Is it a difficult problem? If there were such an alternative, all they would need to do is wait until gmail fouls up, as they did here. Then they'd have a flood of new users. I can imagine a few reasons why there currently isn't an alternative, like network effects stemming from your contact list, or the fact that you'd have to change your email address eve…
The "killer feature" of Gmail that people generally cite is its spam filtering, and that is hard to replicate, because one reason Google's spam filters are so good is because they have an enormous corpus of messages at hand to train them with. This presents would-be competitors with a chicken-and-egg problem: you need lots of users to be able to pull together a corpus like that, but you can't attract lots of users wi…
Also they seem to engage in very spammer-friendly activities such as notifying spammers if and when you read their spam email (if images are turned on by default). Soooo, I can't imagine that competing against their spam filtering is as impossible as people tend to believe.