In terms of users they obviously are the market leader. I use Outlook.com personally and consider it to be overall better than Gmail. I'd gladly debate this if you'd like.

Never the less, my original point was that all of these Gmail strengths that you think are very important are obviously not very important to people using Yahoo or their ISP webmail. The idea that everyone uses Gmail and any competitor must compete feature-by-feature is just incorrect.

This sounds an awful lot like telling your customers they're wrong. And if you find yourself doing that, it's usually because you don't understand what your customer wants.

"obviously are the market leader"

Gmail only just recently (October 2012) overtook Hotmail.

Typo on my part, meant to say that Gmail isn't the market leader in terms of users, Yahoo is.

Is market leader defined in terms of quality/features? Or number of users?

Market leader would mean number of users most likely. Otherwise it's an opinion on which is a better email client and service.

Gmail may be a leader in the US, but Hotmail does have a much larger market penetration in Asian countries. And in the UK, form what I recall.

when i looked for a replacement for gmail, http://www.runbox.com seemed best, but that was a couple of years ago (instead i use procmail, mutt and mairix, but i imagine that's not for everyone...)

huh. has hn always inlined links? maybe i have never added the http: prefix before...?