====== Why can't I send mails with Outlook, Outlook Express or Windows Mail? ======

Outlook, Outlook Express and Windows Mail require LOGIN SMTP authentication mechanism. This is disabled by default.

Edit /etc/postfix/main.cf and change the line 
<code>
smtpd_sasl_security_options = noanonymous, noplaintext
</code>
into 
<code>
smtpd_sasl_security_options = noanonymous
</code>

Now run 
<cli>
# /etc/init.d/postfix reload
</cli>
to reload postfix.

Test this with
<cli>
# telnet your-server 25
</cli>
and type ''ehlo client''

Postfix should respond with
<code>
...
250-AUTH NTLM PLAIN CRAM-MD5 LOGIN DIGEST-MD5
250-AUTH=NTLM PLAIN CRAM-MD5 LOGIN DIGEST-MD5
...
</code>

The AUTH-lines should list PLAIN and LOGIN and Outlook SMTP authentication should work fine now.