@plym @RustyBertrand there's some research into this and it only works something like 1 in 10 times, authors move institutions regularly which makes addresses on papers obsolete, leave academia, and more often than not, don't bother replying, sadly. It's a poor substitute for academics behaving ethically and publishing gold/diamond open access in the first place (which is *always* possible, despite the inevitable moaning from a few extraordinarily out of date folks).