"Strange" maillog entries - am I being used as a relay?

[Mike Pelley <mike pelleys com>]

Folks - I noticed some strange errors in my logwatch report and when I 
checked my maillog I found the entries below.  I have SMTPS with TLS set 
up for authentication.  Does this mean I'm being used as a relay?

maillog:Mar 29 09:30:24 zeus postfix/smtpd[26863]: connect from 
unknown[216.113.195.131]
maillog:Mar 29 09:30:24 zeus postfix/smtpd[26863]: setting up TLS 
connection from unknown[216.113.195.131]
maillog:Mar 29 09:30:24 zeus postfix/smtpd[26863]: TLS connection 
established from unknown[216.113.195.131]: TLSv1 with cipher 
DHE-RSA-AES256-SHA (256/256 bits)
maillog:Mar 29 09:30:25 zeus postfix/smtpd[26863]: 0A1267031D: 
client=unknown[216.113.195.131]
maillog:Mar 29 09:30:25 zeus postfix/smtpd[26863]: 0A1267031D: reject: 
RCPT from unknown[216.113.195.131]: 450 <internal user>: User unknown in 
local recipient table; from=<> to=<internal User> proto=ESMTP 
helo=<email.noproblemnetworks.com>
maillog:Mar 29 09:30:27 zeus postfix/smtpd[26863]: disconnect from 
unknown[216.113.195.131]

Thanks,
Mike