I'm having trouble trying to configure a SPF record in the DNS settings of my domain.
I have created a TXT record with a what should be a valid SPF record.
When I test my domain's DNS setting using http://mxtoolbox.com/domain/ it reports that:
A Valid TXT Record was not found
and
A Valid SPF Record was not found
even though I have definitely set a TXT record and I'm pretty sure the SPF record is valid.
Here are the DNS settings I am using:

Besides this the SMTP seems to be functioning properly.