Install DKIM and SPF in cPanel:
Both the DKIM and SPF authentication functions require the server to be a DNS server for the domain name.
DKIM helps verify the sender and integrity of a message. It allows an email system to prove that a message was not altered during transit (meaning it is not forged), and that the message came from the specified domain.
SPF attempts to prevent spammers from sending email while forging your domain’s name as the sender (spoofing). This authentication function works by adding IP addresses to a list, specifying computers that are authorized to send mail from your domain(s). It verifies that messages sent from your domain(s) are coming from the listed server, reducing the amount of backscatter you receive.
Command to enable DKIM and SPF for cPanel user.
# /usr/local/cpanel/bin/dkim_keys_install cPanelusername
# /usr/local/cpanel/bin/spf_installer cPanelusername
If you would like to enalbe DKIM and SPF for All the user at a time
# for user in `ls -A /var/cpanel/users` ; do /usr/local/cpanel/bin/dkim_keys_install $user && /usr/local/cpanel/bin/spf_installer $user ; done