It seems that `pid` can be the email address only.

* http://doi.crossref.org/servlet/query?pid=y.b@cern.ch&id=10.2331/suisan.32.804&format=unixsd
* http://www.crossref.org/openurl/?pid=y.b@cern.ch&id=10.2331/suisan.32.804&redirect=false