If you have forget to add SPF and DKIM while creating accounts, there is cpanel script available to create SPF and DKIM for existing accounts.
script to enable SPF# /usr/local/cpanel/bin/spf_installer $username
Where $username is the account name of your cPanel account
script to enable DKIM# /usr/local/cpanel/bin/dkim_keys_install $username
Where $username is the account name of your cPanel account
To do this in bulk we can use a simple for loop. Use the following script:
for username in `ls -A /var/cpanel/users` ; do
/usr/local/cpanel/bin/dkim_keys_install $username &&
/usr/local/cpanel/bin/spf_installer $username ; done
That's it.