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example.com. TXT "v=spf1 mx -all"

The difference here is that mx has been added to indicate that any servers tied
to this domain may send email.

Many more variations of SPF records are available. Itemize what you have
and then read the specification at www.openspf.org/SPF_Record_Syntax to
learn what you need to write.

Setting Up a DNS Server with BIND

The Berkeley Internet Name Domain (BIND) software has been foundational
to the Internet since the 1980s. The original BIND was created at the
University of California, Berkeley, using grant funding. It was released as free
and open source with the BSD (Berkeley Software Distribution) version of
UNIX and was quickly adopted as the standard software for DNS. The
Internet Systems Consortium now maintains BIND and provides updates and
documentation at www.isc.org.

When you create NS records for your domains with your domain name
registrar, pointing at ns1.domainregistrationcompany.com or
whatever domain the registrar gives you, you are most likely pointing to a
server running BIND, although other options exist. This section shows how to
install and set up a very basic DNS server using BIND.

Start by installing bind9 from the Ubuntu software repositories.

Next, use your favorite text editor to open
/etc/bind/named.conf.local, which is a configuration file set up
with default settings. This is where you must declare the zones you are setting
up and associating with the domain. Zones are domain names that are
referenced in the DNS server. Leave all the default text in the file and add this
to the end of the file, after replacing example.com with your domain name:

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This is the zone definition.

zone "example.com" {
type master;
file "/etc/bind/zones/example.com.db";
};

Save the file and exit.

Next, open the configuration options file at
/etc/bind/named.conf.options and modify the section titled