Logs:
Apr 28 08:36:00 backup postfix/pickup[12743]: 7B13D9A067: uid=1000 from=<car>
Apr 28 08:36:00 backup postfix/cleanup[12815]: 7B13D9A067: message-id=<20110428133600.GA12801@austin.bio-west.com>
Apr 28 08:36:00 backup postfix/qmgr[12744]: 7B13D9A067: from=<car@austin.bio-west.com>, size=435, nrcpt=1 (queue active)
Apr 28 08:36:00 backup postfix/smtp[12817]: 7B13D9A067: to=<rock@peppa.com>, relay=smtp.sbcglobal.yahoo.com[68.142.198.11]:587, delay=0.27, delays=0.01/0.01/0.22/0.04, dsn=5.0.0, status=bounced (host smtp.sbcglobal.yahoo.com[68.142.198.11] said: 553 From address not verified - see http://help.yahoo.com/l/us/yahoo/mail/original/manage/sendfrom-07.html (in reply to MAIL FROM command))
Apr 28 08:36:00 backup postfix/cleanup[12815]: CFBE69A06B: message-id=<20110428133600.CFBE69A06B@austin.bio-west.com>
Apr 28 08:36:00 backup postfix/bounce[12818]: 7B13D9A067: sender non-delivery notification: CFBE69A06B
Apr 28 08:36:00 backup postfix/qmgr[12744]: CFBE69A06B: from=<>, size=2515, nrcpt=1 (queue active)
Apr 28 08:36:00 backup postfix/qmgr[12744]: 7B13D9A067: removed
Apr 28 08:36:01 backup postfix/smtp[12817]: CFBE69A06B: to=<car@austin.bio-west.com>, relay=smtp.sbcglobal.yahoo.com[68.142.198.11]:587, delay=0.16, delays=0/0/0.13/0.02, dsn=5.0.0, status=bounced (host smtp.sbcglobal.yahoo.com[68.142.198.11] said: 501 Syntax error in arguments (in reply to MAIL FROM command))
Apr 28 08:36:01 backup postfix/qmgr[12744]: CFBE69A06B: removed

Postfix Config:
# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = austin.bio-west.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = localhost
relayhost = [smtp.sbcglobal.yahoo.com]:587
mynetworks = 127.0.0.0/8 10.1.1.0/24

mailbox_command = 
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only

smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

# smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
# smtp_sasl_security_options = noanonymous
inet_protocols = ipv4