Reading, sending and client navigability
Sparrow and Airmail give you the option of a floating composition window or a shallow Twitter-like window for quick replies. When you’ve finished typing, Airmail lets you send and archive a thread with a single click. It also lets you drag messages (to the trash, for example), which Sparrow doesn’t, and set them as To Dos or Memos, for later viewing. Postbox can convert messages to To Dos, and as with Thunderbird, lets you drag messages to folders. You can set Thunderbird to ignore whole threads (if you get copied in on a long cc’d conversation you don’t want to follow), and it tops off emails with ‘archive’ and ‘junk’ buttons, so you can quickly zap them. Unibox also has these buttons, but being contact- rather than inbox-focused, filing messages to folders takes a couple of extra clicks through some drop-down menus. Inky has menus of folders for filing, and also tries to guess email relevance, sorting them by rank. If it gets this wrong, you can bump a message score up or down for future reference.
Sparrow’s neat interface gives the option of full or compact compose windows.