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

smtpd_sasl_security_options = noanonymous, noplaintext

into

smtpd_sasl_security_options = noanonymous

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

...
250-AUTH NTLM PLAIN CRAM-MD5 LOGIN DIGEST-MD5
250-AUTH=NTLM PLAIN CRAM-MD5 LOGIN DIGEST-MD5
...

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