SSL Certificate

Hi all,

I'm managing a mail server, which doesn't have any SSL Certificate.
However, if I try to connect with a secure connection using POP3 on port 995, I'm able to download and send emails.

I obviously get the message saying that the SSL Certificate is not trusted, but I don't understand why it works.

The server doesn't even have an SSL Certificate to trust.
Is the connection encrypted on a public key created by the server, but not trusted? Or is it not even encrypted?

Thanks!