Citadel not sending encrypted emails

Hi there,
I' trying to set up a mailserver on my new Ubuntu 14.04 VPS. I've chosen Citadel. The purpose is to have Citadel both handle incoming and outgoing emails. I've kind of achieved what I needed, but the problem I'm facing now is that Gmail tells emails sent from the VPS are unecrypted.

Schermata del 2016-07-16 07-15-45.png

I'm quite new to setting this up so feel free to ask any questions, since I don't really know what details to provide. I will say that even though all Citadel ports should be open, the firewall is disabled right now, as to clear any possible issues coming from it.

Hope someone has a clue and can help, huge thanks!

- - , .
.