uses back ticks not quotes. I mentioned a NAT device in my earlier post, are you behind a router and if so is there a local DNS server?
If I lookup your DNS here and telnet to the pointed to IP it shows another mailserver running:
I would guess your DNS is incorrectly set-up and/or you need to disable the other mailserver.
telnet mobecservices.com 25
Connected to mobecservices.com.
Escape character is '^]'.
220-serv01.siteground139.com ESMTP Exim 4.66 #1 Tue, 15 May 2007 10:20:42 -0500
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.