If you want to add SPF records for all cPanel accounts on CentOS Linux server then cPanel makes it easy, as it has provided with script through which you can add SPF records on cPanel accounts at once.
First of all you have to login as root on cPanel server. Then you have to run this command for adding SPF record for an cPanel user account :
Here, you have to use actual username in place of cpanelusername.
Now if you want to enable it for all accounts on your server then the above process will be too time consuming. You can do it for all account at once through the custom script given below.