By far the most well designed and feature rich mail application that I have used so far, all of its simple design, support for multiple accounts and a multitude of nice shortcuts that you can use.
I approach all of my email tasks in GTD style. Keeping my email inbox close to 0 at all times.
Airmail provides good set of onscreen keys that you can use to do various actions on mails.
I also automatically sort newsletters into mailboxes so they never show up in my Inbox and I have to visit my
News mailbox whenever I want to read these emails. This is a rule set of how you can set it up for yourself:
And here is my sidebar of labels I use for my email accounts:
The main goal is that the only emails that can get into my Inbox are emails from real people that are actionable and ideally important. Anything else should be sorted automatically or not sent in the first place. Unsubscribe from anything that brings no value and only adds noise.