I need to install postfix on my webserver couse I need to use sendmail for my website. I only need to send mail not recieve or relay.

send with starttls (port 587) via relay smtp.strato.de

here is what happens

Jul 15 00:02:38 negrita postfix/smtp[7120]: Host offered STARTTLS: [smtp.strato.de]
Jul 15 00:02:38 negrita postfix/smtp[7120]: C717A181252: to=<[email protected]>, relay=smtp.strato.de[81.169.145.133]:587, delay=0.31, delays=0.09/0/0.16/0.04, dsn=5.7.0, status=bounced (host smtp.strato.de[81.169.145.133] said: 530 5.7.0 Bitte konfigurieren Sie ihr E-Mailprogramm fuer Authentifizierung am SMTP Server, wie auf www.strato.de/email-hilfe beschrieben. - Please configure your mail client for using SMTP Server Authentication (in reply to MAIL FROM command))
Jul 15 00:02:38 negrita postfix/cleanup[7118]: 29F5F181254: message-id=<20120714220238.29F5F181254@negrita>
Jul 15 00:02:38 negrita postfix/qmgr[7102]: 29F5F181254: from=<>, size=2548, nrcpt=1 (queue active)
Jul 15 00:02:38 negrita postfix/bounce[7121]: C717A181252: sender non-delivery notification: 29F5F181254
Jul 15 00:02:38 negrita postfix/qmgr[7102]: C717A181252: removed
Jul 15 00:02:39 negrita postfix/local[7122]: 29F5F181254: to=<michael@negrita>, relay=local, delay=1.1, delays=0.04/0/0/1.1, dsn=2.0.0, status=sent (delivered to command: procmail -a "$EXTENSION")
Jul 15 00:02:39 negrita postfix/qmgr[7102]: 29F5F181254: removed
Jul 15 08:05:18 negrita postfix/master[1083]: daemon started -- version 2.9.1, configuration /etc/postfix
Jul 15 08:05:29 negrita postfix/master[1083]: reload -- version 2.9.1, configuration /etc/postfix

and my config

michael@negrita:~$ postconf -n
biff = no
config_directory = /etc/postfix
delay_warning_time = 4h
home_mailbox = /home/michael/Maildir/
html_directory = /usr/share/doc/postfix/html
inet_interfaces = localhost
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
mydomain = example.com
myhostname = negrita
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
notify_classes = resource, software, protocol
readme_directory = /usr/share/doc/postfix
recipient_delimiter = +
relayhost = [smtp.strato.de]:587
smtp_sasl_password_maps = hash:/etc/postfix/sasl/passwd
smtp_tls_enforce_peername = no
smtp_tls_note_starttls_offer = yes
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes
soft_bounce = yes

the user and password is ok couse I can send mail with my thunderbird

thanks in advance mike