Here is the output when I send the mail using webmail (Roundcube):
Dec 14 11:26:10 molenwiek-it postfix/smtpd[24903]: 67A7A91D59: client=localhost[::1], sasl_method=PLAIN,
[email protected]
Dec 14 11:26:10 molenwiek-it postfix/cleanup[24414]: 67A7A91D59...