WD removed remote drive mapping when they released the OS3 firmware last year. Officially there is NO replacement or workaround from WD for remote access other than to use; the WD apps/software, the My Cloud.com web portal, or enable FTP.
Unofficially, see the following link to setup WebDAV on v4.x My Cloud’s which will allow for remote mapping of the My Cloud and also offers a web interface to access the files of the My Cloud. Works quite well.
https://community.wd.com/t/app-clouddavmod-v1-0-for-firmware-v4-04-2016/161543
Feel free to voice your opinion of WD removing the remote drive mapping in the following Cloud Ideas thread:
https://community.wd.com/t/re-enable-remote-drive-mapping-through-mycloud-com/134944
