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See chapter 3 of DOI handbook https://www.doi.org/doi_handbook/3_Resolution.html section 3.7.3

Alternatively, without the need to extend their web browsers' capability, users may resolve DOI names that are structured to use the DOI system Proxy Server (http://doi.org (preferred) or http://dx.doi ...

Simple as that, I am ashamed Thank you! It works, you made my day. ač

According to https://www.doi.org/doi_handbook the new and prefered URL syntax for doi:10.123/456 is http://doi.org/10.123/456 (while an earlier syntax http://dx.doi.org/10.123.456 is fully supported but no longer preferred).

I work on Ubuntu 16.04 and use pdflatex (pdfTeX 3.14159265-2.6-1.40.16 TeX ...