this is from the SquirrelMail webmail that is using smtp as default
ERROR:
Authentication required
Server replied: 530 5.7.0 Must issue a STARTTLS command first
sending email from a external MUA
May 28 18:48:38 ashley postfix/smtpd[4288]: connect from ashley.tuxblogger.nl[84.245.7.46]
May 28 18:48:38 ashley postfix/smtpd[4288]: setting up TLS connection from ashley.tuxblogger.nl[84.245.7.46]
May 28 18:48:41 ashley postfix/smtpd[4288]: TLS connection established from ashley.tuxblogger.nl[84.245.7.46]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)
May 28 18:48:41 ashley postfix/smtpd[4288]: 9634E83D3: client=ashley.tuxblogger.nl[84.245.7.46], sasl_method=PLAIN, sasl_username=jelle@tuxblogger.nl
May 28 18:48:41 ashley postfix/cleanup[4296]: 9634E83D3: message-id=<465B0818.1070804@tuxblogger.nl>
May 28 18:48:41 ashley postfix/qmgr[4286]: 9634E83D3: from=<jelle@tuxblogger.nl>, size=655, nrcpt=1 (queue active)
May 28 18:48:42 ashley postfix/smtpd[4288]: disconnect from ashley.tuxblogger.nl[84.245.7.46]
May 28 18:48:42 ashley postfix/smtp[4298]: 9634E83D3: to=<jelle@tuxblogger.nl>, relay=127.0.0.1[127.0.0.1]:10024, delay=0.49, delays=0.36/0.06/0.08/0, dsn=4.7.4, status=deferred (TLS is required, but was not offered by host 127.0.0.1[127.0.0.1])
relay=127.0.0.1[127.0.0.1]:10024 << local and wants TLS :-S