tons of hits to /404/<article permlink>/wp-mail.php?referer=<article permlink>

I have a standalone wordpress installation on godaddy. For many articles I get a lot of hits on 404 pages generated like the example below:
https://www.raheazadi.com/404/1388/06/11/ayatollah-mesbah-yazdi-sodomy-and-rape-of-protesters-is-ok/wp-mail.php?referer=https://raheazadi.com/1388/06/11/ayatollah-mesbah-yazdi-sodomy-and-rape-of-protesters-is-ok/

I am not sure how these links are created or how the visitors are reaching them. I have sociable plugin installed for people to email posts for example and that seems to work always (I tried it on multiple browsers). I would really appreciate if anyone could help me figure out how visitors are reaching these links.