How do i setup cPanel server to send emails?

Hi,

My port 25 is open for Linode server, so i can have domains sending emails. I will be using Linode server for shared hosting environment for 100+ cPanel accounts. It looks like I have to add SPF record on each domain: example.com TXT "v=spf1 a ~all" in WHM/cPanel to be able to send emails.

Now, I have people signing up and canceling, I have to check daily how which domain doesn't have SPF record so I can add it manually…. That's a lot of time consuming. Is there any other way, workaround to apply this SPF on a server-side so any existing and new accounts have it by default?

I would appreciate help from anyone using the same concept with cPanel for shared hosting environment and advice on how to set up all domains to send emails.

Thanks