Port 465 is the SMTPS port, SMTP over SSL. As such, your probably want to use the
openssl tool rather than telnet if you are trying to debug SMTP. This won't solve your original issue though, which is that the remote host is immediately disconnecting you. This may be due to it only allowing connections from certain addresses. The way this is implemented is to accept connections and then close them if they don't originate from an accepted IP address. I would need more details on the SMTP server you are using, and its configuration, to help you more than that.
openssl s_client -connect remote.host:465