There is such nice thing as Gmail Inbox Actions: https://developers.google.com/gmail/actions/ , that allow to put custom links next to the message in inbox in Gmail. These links for example can be used to view associated commit, issue or anything else which caused e-mail to be sent.
See how GitHub has used these: https://github.com/blog/1891-view-issue-pull-request-buttons-for-gmail
It would be great to have support for them in Phabricator as well.