[Dovecot] auth attempts errors

i have install 2.1.1 and configured

in dovecot log this error is coming every 20 seconds:

dovecot: imap-login: Disconnected (no auth attempts in 0 secs): rip=**********, lip=**********, TLS handshaking: SSL_accept() syscall failed: Connection reset by peer

and this error every 2 seconds:

dovecot: imap-login: Disconnected (no auth attempts in 0 secs): rip=**********, lip=**********

what can be the problem?

thanks..