Failed to start stunnel4 on Ubuntu 15.04

Is this 212.43.222.123 really your server's ip address, or are you NAT'd behind something? If you're NAT'd then your accept = needs to point to your LAN ip.

What is the output of ifconfig?

Or I wonder if the /etc/services/ file is preventing you from binding port 443 to a service other than https; If that's really the ip address, try commenting out the 2 lines referencing 443 in /etc/services then restart stunnel4 again.

default /etc/services lines:

https           443/tcp                         # http protocol over TLS/SSL
https           443/udp

after change:

#https           443/tcp                         # http protocol over TLS/SSL
#https           443/udp