When writing an email about Emacs, e.g. on the help-gnu-emacs mailing list, I often want to include a link to an Info node. It is easy in Org-mode, where you can use org-store-link (however, by default, the link does not export “properly” to HTML, though, i.e., you don’t get the link to the online Emacs manual) and then org-insert-link. But even if you don’t use Org-mode, there is a nice trick: you can press c in any info buffer to copy the “link” (i.e., the current node name) to the kill buffer. Then, you can write
(info "<yank here>")
in your email, and tell the recipient to position the point after that form and press C-x C-e. (In case s?he does not use Emacs to read mail, s?he will have to copy it to *scratch* or somewhere first, of course.)