What are the SPF records?
A Sender Policy Framework (SPF) record is a type of Domain Name Service (DNS) TXT record that identifies which mail servers are permitted to send an email on behalf of your domain. The purpose of an SPF record is to detect and prevent spammers from sending messages with forged From addresses on your domain.
Sender Policy Framework (SPF) is a method of fighting spam. As more time passes, this protocol will be used as one of the standard methods of fighting spam on the Internet. An SPF record is a TXT record that is part of a domain’s DNS zone file. The TXT record specifies a list of authorized hostnames/IP addresses that mail can originate from for a given domain name. Once this entry is placed within the DNS zone, no further configuration is necessary to take advantage of servers that incorporate SPF checking into their anti-spam systems. This SPF record is added the same way as a regular A, MX, or CNAME record.
Collect all IP addresses that are used to send email
The Sender Policy Framework (SPF) gives the ability to authenticate your email and to specify which IP addresses are allowed to send an email on behalf of the specific domain.
In order to successfully implement SPF, you first need to identify which mail servers are used to send an email for your domain. These mail servers can be any sending organization, you should think of your Email Service Provider, Office mail server and any other third-party mail servers that may be used to send an email for you.
Create your SPF record
v=spf1 ip4:18.104.22.168 ~all
named (bind DNS server) config
@ IN TXT "v=spf1 a mx ~all"