I have now added the DNF IP address to my white list and emails are coming through fine now.
In response to a few PM's
A whitelist is the opposite of a blacklist, whereas you would add the IP address of the server you would like to approve, servers on the whitelist do not get processed through your SPAM software.
GMAIL users can approve the
[email protected] email address so that it wont get dropped into SPAM folder.
If you are unsure as to what it is then please contact your ISP and get them to add the DNF ip address you their whitelist.