How should I configure postfix to avoid sent emails bouncing because of "Invalid HELO name"

Some mail sent from sites on my server bounce back with the following mail.log message

Nov 26 17:27:53 blogu postfix/smtp[16858]: C4DD22908EC0: to=, relay=rejecting-domain.ro[rejecting-ip]:25, delay=2.5, delays=0.1/0/2.3/0.04, dsn=5.0.0, status=bounced (host rejecting-domain.ro[rejecting-ip] said: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1) (in reply to MAIL FROM command))

On the receiving end, my emails are logged like this:

2011-11-22 15:09:35 H=static.39.80.4.46.clients.your-server.de (Ubuntu-1004-lucid-64-minimal) [my-server-ip] rejected MAIL : Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

Solution 1:

Ubuntu-1004-lucid-64-minimal is not a valid global name, tell postfix to use your "real" domain name, using the myhostname setting: http://www.postfix.org/postconf.5.html#myhostname