Email account vertification doesn't work

[SystemFiles]

Hey guys,

I am not able to get my email send out when a user registers. "Verify Email address in Registration" I've set to yes.

So what I tried is going under Maintenance > Diagnostics > Email. And I actually did recieve an email.

So after that I tried to enable "Enable '-f' Parameter" and that also didn't work, but I did recieve a message on the administrator mail.

Reporting-MTA: dns; n1nlhg03125.shr.prod.ams1.secureserver.net
Received-From-MTA: DNS; localhost
Arrival-Date: Sat, 24 Aug 2013 06:26:43 -0700

Final-Recipient: RFC822; xxx@gmail.com
Action: failed
Status: 5.0.0
Remote-MTA: DNS; relay-hosting.secureserver.net
Diagnostic-Code: SMTP; 554 mail server permanently rejected message (#5.3.0)
Last-Attempt-Date: Sat, 24 Aug 2013 06:26:44 -0700

Anybody has an idea on how to figure this out since I really need this feature in order to prevent those constant spambots from signing up at my forum.

Regards,
SystemFiles