E-Mail Users Problem

I have a problem and seem i cannot get any help from vBulletin team or support team from my server as both claims the problem is on the other side.

When i try to send e-mails from admincp > users > e-mail users nearly 95% of the e-mails are returning. When i use admincp > diagnosis > send e-mail it works pretty good. So does anyone have any idea what can cause this or how i can get a solution for this ?


Return errors look like (edited e-mail adresses for privacy) :

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxx@gmail.com
unrouteable mail domain "gmail.com"


his message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxx@hotmail.com
unrouteable mail domain "hotmail.com"

Looks like a problem with your ISP/mail server.

Originally Posted by Keith Cohen

Looks like a problem with your ISP/mail server.

And they claim mail server works pretty good. Do you have any idea where shall i ask them to look at ?