IP Masquerade and Network Address Translation

http://www.oreilly.com/openbook/linag2/book/ch11.html

The Beginner’s Guide to iptables, the Linux Firewall

https://www.howtogeek.com/177621/the-beginners-guide-to-iptables-the-linux-firewall/

Tutorial: Installing OpenVPN on Ubuntu 16.04

How To Install OpenVPN On Ubuntu 16.04

To configure iptables look here:

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-16-04

 

How to Configure OpenVPN Access Server to Tunnel Traffic

https://linode.com/docs/networking/vpn/configure-openvpn-access-server-to-tunnel-traffic/

Install OpenVPN Access Server on Linux for Secure Communications

https://linode.com/docs/networking/vpn/install-openvpn-access-server-on-linux/

Install Roundcube on Ubuntu 16.04

https://linode.com/docs/email/clients/install-roundcube-on-ubuntu/

A Few Great Ways to Consume RESTful API in C#

https://www.codeproject.com/Articles/1190592/A-Few-Great-Ways-to-Consume-RESTful-API-in-Csharp