If I telnet to my mail server, and do not issue any command just the QUIT, I get the same logs. (except the NOQUEUE: at the beginning.)
The NOQUEUE i get when my server denies the connection.
This means that the client application (MUA) which is connecting to the server do not start any authentification, or action on your server...
I dont know if it helps you ...
How do you configure your sendmail server, directly with M4 or use some other application??