I used to work at MS and the Fax team was a part of the Print Spooler team until the print team got reorged after Windows 7.
The Fax stuff was moved to another country but really never had any owner since mid 2011.
I expect that to still be the case. I hope I am wrong.
If you actually pay some funds to MS, I am sure someone can dig up the answers but even in 2012, from the print teams perspective Fax was dead so never got any love.
Thanks