Got Got Background Task email error notice

Hi,

Got Background Task email error notice:

The following Background Task did not complete successfully:

Date/Time

:

2015-09-08 14:30:06

Activity

:

Newsletter Mailer

Summary

:

Returned errors

Completed

:

0

Function

:

nlb_mailer

Output

:

Adding messages to the queue for scheduled sent newsletter message #23

Sending queued 'Background Send' emails, (7 queued, sending max 500 per batch)

Sending message to xxxxxxxxxxx
No messages were sent, check mail server settings!
Email delivery failed for: xxxxxxxxxxx

Runtime

:

0.98 seconds

Please check the Background Tasks logs here and check for additional errors:
http://www.xxxxxxxxxxx.com/cmsAdmin/admin.php?menu=_cron_log

You can review the Background Tasks status & settings here:
http://www.xxxxxxxxxxx.com/cmsAdmin/admin.php?menu=admin&action=general#background-tasks

*Please note, incomplete background task alerts are only sent once an hour.

How to fix the error?

Thanks!