Please help with SPF record in sever

Hello

We bought a domain and create a mail2.mydomain.com to configure a mail server. But when we send mails through it,, the mails go directly to spam or not arrive. My cpanel domain have enabled the SPF but still the same problem. So, my provider told me that we have to enable in the SERVER the SPF and I cant find where to enable this. I have sent mails to apple directly and still waiting for their answers so please can anyone help me (step by step) where to find and enable that spf in the server please.

Regards