5 5 4 Invalid ESMTP parameter

I cannot send Emails.
The system tells: it was a misstake: 5.5.4 Invalid ESMTP parameter
What mean this?
I can get Emails, but not sent.
Who can help?
Thanks!
Andrea

Hi,
are you authenticating with the server? Please check the account settings and let me know if you have enabled authentication. Thank you.