How to enable port 25 on my Ubuntu server?

So I am running Spree e-commerce in Rails. When I click on ‘place order’ after I have added items to my cart and proceed to checkout i got this error. (same question as this person)

Errno::ECONNREFUSED in Spree::CheckoutController#update
Connection refused - connect(2) for "localhost" port 25

I believe it has something to do with the email but I am not 100 percent sure. As for spree is defaulted to port 25 as referred to here

I checked my port using

telnet mydroplet'sIPaddress 25

and it said (as expected)

telnet: Unable to connect to remote host: Connection refused

I tried a solution to unblock my port 25 by adding the line below as suggested in another question here.

iptables -I INPUT -p tcp -m tcp --dport 25 -j ACCEPT

and recheck using the same method and still no good.

I even went to setup my firewall using ufw and made sure my port 25 is available by following this tutorial

sudo ufw allow 25/tcp

still no good…

PLEASE HELP!

How do I enable my port 25?

I am running Ubuntu Ruby on Rails on 14.04 (Postgres, Nginx, Unicorn).

My IP address is 128.199.95.219 if anyone wants to try my port 25.