SMTP Error: Data not accepted

Out of 1600 something subscribers my Newsletter was only sent to 9! I get the following error:

“SMTP Error: Data not accepted.

The transmission process was stopped because there was too many errors.
All emails that are not sent ended up in a queue so that you can continue the transmission later.
Please verify your settings for sending e-mail and make sure you can send a test of this e-mail.
If you previously managed to send out multiple e-mail, the error may be due to your server’s capabilities.”

This is my first multiple e-mail list, so I have not been successful in sending out any newsletter yet.
Test mail ok, but with this notice:

Notice: mail(): Policy restriction in effect. The fifth parameter is disabled on this system in /customers/e/2/c/valet.se/httpd.www/wp-content/plugins/wysija-newsletters/inc/phpmailer/class.phpmailer.php on line 537

I am sending from my own website.

What can I do?!