stunnel latest verstion installation in ubuntu

To Installation

$ sudo apt-get install stunnel4

Then Enabling run stunnel at startup

$ vi /etc/default/stunnel4
Change

ENABLED=0
to
ENABLED=1

Otherwise, you will get below error,
SSL tunnels disabled, see /etc/default/stunnel4

Then Configure stunnel
Copy default copy of configuration stunnel.conf from stunnel examples directory as below,

$ sudo cp /usr/share/doc/stunnel4/examples/stunnel.conf-sample /etc/stunnel/stunnel.conf
Create an open certificat to run stunnel
Generate the certification with oppenssl
$ sudo openssl req -new -out mail.pem -keyout mail.pem -nodes -x509 -days 365

Type and fill all the question it ask and it will generates a certificate that is valid for 365 days.
Then open and edit the config file stunnel.conf

$ vim /etc/stunnel/stunnel.conf
add the path where we create certificate mail.pem

; Certificate/key is needed in server mode and optional in client mode
cert = /etc/stunnel/mail.pem
;key = /etc/stunnel/mail.pem

then add below lines to setup for gmail.

[gmail]
accept=192.168.1.100:25
connect=smtp.gmail.com:465

save and write the file.(:wq!)

stop and restart stunnel
$ sudo /etc/init.d/stunnel4 stop
$ sudo /etc/init.d/stunnel4 start
Or
$ sudo /etc/init.d/stunnel4 restart

:)

check service is working or not by below command

service --status-all

and check port is listening status

sudo netstat -ntlp | grep LISTEN
or
nmap <IP address of stunnel machine>

if nmap is not installed, install it by

apt-get install nmap


At last check the it is listening port 25 use telnet from same machine or any other machine

telnet 127.0.0.1 25

or from other system
telnet 192.168.1.100 25

If telnet client is not installed in ubuntu machine ,install by

sudo apt-get install xinetd telnetd

If telnet is getting responds from port 25, then connection is successful.

If your getting "Could not open connection to the host, on port 25
: Connect failed" message then need to reconfigure stunnel service again.

:)