Answer by Denis Chomaryan for Copy link to message by RFC 822 Message-ID, e.g., via Chrome Extension or Gmail Labs

You can use a Chrome bookmarklet.

Make a bookmark at a panel with the following code in the URL field:

javascript:window.location="https://gmail.com/#search/rfc822msgid:"+encodeURIComponent(window.document.body.innerHTML.match(/Message-ID: <(.*)>/)[1])+"/"+encodeURIComponent(window.location.search.toString().slice(1).split('&').filter(function(x){return x.slice(0,3) == "th="})[0].slice(3));

Then in Gmail you should open an original code of a message (from the menu in the right top corner of a message block) and click the bookmarklet. It will open a new tab with a generated URL with message id that you can copy with hotkeys.

This method isn't very handy and needs a couple of actions just to copy the link, but it's the only solution I've found by now.

I'm already about writting my Chrome extension to make it in one click, but it needs free time for developing.