Airmail is a well-known, well-received email client on Macs. But when you have a huge screen, keyboard and mouse, a good email app on the desktop doesn’t have to try so hard. However, making a good email app on a smartphone is a whole different can of worms. So here’s Airmail for iPhone, which launched last week. It gives you all kinds of ways to deal with (or delay) the email problem, and it’s claimed a space in my hallowed four-space iPhone dock. No more Mail, and no more Gmail.I have two email accounts: my personal Gmail account and my Engadget address (which is also powered by Google). While I don’t have many inboxes, though, I do have a few legacy email addresses that auto-forward to the main Gmail address. It’s not a complicated or elaborate setup, but I lean heavily on email for work, travel, organizing app-based notifications (Twitter, Facebook, Amazon etc.) and communicating with folks back home. (I live overseas.) And because I deal with email throughout the workday, I’m willing to pay to make it easier. Specifically, $4.99 for the download. I’m likely to be in the minority, however.It’s hard for email apps on the iPhone to make it big. Given that the preinstalled email app doesn’t do a bad job, and there’s no shortage of challengers, it’s hard for any single contender to break through, much less one you have to pay for. We’ve seen Dropbox’s Mailbox appear and disappear despite a handful of clever ideas, and Google’s Inbox-made automated responses aren’t perfect — and then you’re already splitting a fraction of users away from the Gmail app itself.