How do I open a thread / message in another window?

We are phasing out Zendesk. Please see Discourse instead: https://community.getmailspring.com/t/open-message-in-new-window/292

You can open threads in a new window by double-clicking them in the thread list, or clicking the small "pop out" icon shown beside the subject line along with "Print" and "Expand Thread".

There's currently no way to pop out a folder / label / search results view, but we're hoping to add that in a future release.